UG Applied Mathematics Booster Test 3 - Solutions of Differential Equations
📌 Answers are locked once submitted — results and explanations appear at the end.
QUESTION 1 OF 20
Analytically, if a general solution has 3 arbitrary constants, it represents a differential equation of order 3. If we are given the equation
\(y=c_{1}e^{x}+c_{2}e^{-x}+c_{3}e^{x},\)
what is the actual order of the resulting differential equation?
QUESTION 2 OF 20
Match the multi-parameter function to the order of its corresponding differential equation.
| List I | List II |
|---|---|
| 1. y = a sin(x+b) | a. Differentiate once, substitute to get x + y y' = 0 |
| 2. x² + y² = a² | b. Differentiate twice, yielding y'' + y = 0 |
| 3. y = mx | c. Differentiate twice, eliminate parameters to get x y y'' + x(y')² - y y' = 0 |
| 4. x²/a² + y²/b² = 1 | d. Differentiate once, substitute y/x for parameter |
QUESTION 3 OF 20
In solving the equation
(x+1)dy/dx=2xy
with the initial condition
y(2)=3,
which sequential steps are mathematically correct?
Statements:
A. The separated form is
dy/y=2x/(x+1) " " dx.
B. Integration yields
log∣y∣=2x-2log∣x+1∣+c.
C. The integration requires writing
2x/(x+1)=2-2/(x+1).
D. The constant cevaluates to
log3-4+2log3.
QUESTION 4 OF 20
Identify the INCORRECT statement regarding the particular solution of
dy/dx=x(2logx+1)
with the initial condition
y(2)=0.
QUESTION 5 OF 20
A mixture of parabolas with vertices at the origin and foci on the positive y-axis is represented by
x^2=4ay.
The differential equation for this family of integral curves is:
QUESTION 6 OF 20
Graphically, forming the differential equation for circles having their center on the y-axis and passing through the origin requires establishing the equation
\(x^{2}+(y-a)^{2}=a^{2}.\)
What is the geometric constraint applied when differentiating?
QUESTION 7 OF 20
Sequentially verifying
y=2e^2x-3e^(-x)
for the equation
(d^2 y)/(dx^2 )-dy/dx=2y
requires finding the second derivative. What is
(d^2 y)/(dx^2 )?
QUESTION 8 OF 20
Verifying
y=a+logx
for the equation
x (d^2 y)/(dx^2 )+dy/dx=0
involves tracking the derivatives. The second derivative
(d^2 y)/(dx^2 )
evaluates to:
QUESTION 9 OF 20
What is the probability that implicitly differentiating
(x^2-y^2)dy/dx-2xy=0
is required to verify the family of circles passing through the origin with centre on the x-axis?
QUESTION 10 OF 20
To verify that
x(y (d^2 y)/(dx^2 )ⓜ+(dy/dx)^2 )=y dy/dx
derives from
x^2/a^2 +y^2/b^2 =1,
we differentiate implicitly twice. After the first differentiation, we get
x/a^2 +(y dy/dx)/b^2 =0.
The next crucial vector-like substitution step is:
QUESTION 11 OF 20
To find the bounding function y(x)when
dy/dx=e^x.e^y+x^2 e^y,
factoring out e^ygives
dy/dx=e^y (e^x+x^2).
The separated integrable area form is:
QUESTION 12 OF 20
Integrating the separated form
y/(y+2) " " dy=(x+2)/x " " dx
obtained from the differential equation
xy dy/dx=(x+2)(y+2),
yields:
QUESTION 13 OF 20
13. Algebraically separate the variables for \(x(e^{2y}-1) dy+(x^{2}-1)e^{y} dx=0\):
QUESTION 14 OF 20
After separating
(e^2y-1)/e^y " " dy=(1-x^2)/x " " dx
into
(e^y-e^(-y))" " dy=(1/xⓜ-x)" " dx,
integrating both sides yields:
QUESTION 15 OF 20
Rearranging the complex equation
log(dy/dx)=3x+4y
to solve it requires which initial algebraic manipulation?
QUESTION 16 OF 20
When evaluating the integrated exponential form
e^(-4y)/(-4)=e^3x/3+c,
multiplying by −12 to clear fractions changes the arbitrary constant cto −12c. By convention, this is usually rewritten as:
QUESTION 17 OF 20
The general solution to
log(dy/dx)=3x+4y
after complete integration and rearrangement is:
QUESTION 18 OF 20
For the differential equation
dy/dx=(x+1)/(2-y),
the functional relationship defining the general solution curve family is analytically given by:
QUESTION 19 OF 20
xy dy/dx=(x+2)(y+2).
Separating the variables gives
y/(y+2) " " dy=(x+2)/x " " dx.
Rewrite the fractions as
(1ⓜ-2/(y+2))dy=(1ⓜ+2/x)dx.
Integrating both sides,
y-2log∣y+2∣=x+2log∣x∣+c.
If the required curve passes through the point
(1,-1),
substitute these coordinates into the general solution to determine the value of the arbitrary constant. Substituting this value back into the general solution gives the required particular solution.
x=1,y=-1
into
y-2log∣y+2∣=x+2log∣x∣+c
yields what exact value for c?
QUESTION 20 OF 20
xy dy/dx=(x+2)(y+2).
Separating the variables gives
y/(y+2) " " dy=(x+2)/x " " dx.
Rewrite the fractions as
(1ⓜ-2/(y+2))dy=(1ⓜ+2/x)dx.
Integrating both sides,
y-2log∣y+2∣=x+2log∣x∣+c.
If the required curve passes through the point
(1,-1),
substitute these coordinates into the general solution to determine the value of the arbitrary constant. Substituting this value back into the general solution gives the required particular solution.
\(c=-2,\)
the final particular solution algebraically simplifies to:
Test Complete!
Answer Review
1 Analytically, if a general solution has 3 arbitrary constants, it represents a differential equation of order 3. If we are given the equation
\(y=c_{1}e^{x}+c_{2}e^{-x}+c_{3}e^{x},\)
what is the actual order of the resulting differential equation?
The terms c₁eˣ and c₃eˣ are like terms and can be combined into a single constant multiplying eˣ. Therefore, only two independent arbitrary constants remain, so the differential equation is of order 2.
The given general solution is \(y=c_{1}e^{x}+c_{2}e^{-x}+c_{3}e^{x}.\) Notice that both c₁eˣ and c₃eˣ contain the same function eˣ. Combine them as \(c_{1}e^{x}+c_{3}e^{x}=(c_{1}+c_{3})e^{x}.\) Let \(C=c_{1}+c_{3}.\) Then the solution becomes \(y=Ce^{x}+c_{2}e^{-x}.\) Now there are only two independent arbitrary constants: C c₂ Since the order of a differential equation equals the number of independent arbitrary constants in its general solution, the resulting differential equation is of order 2. Hence, Option B is correct.
- Option A) 3
- Incorrect because the three constants are not independent.
- c₁ and c₃ combine into a single arbitrary constant.
- Option C) 1
- Incorrect because the simplified solution still contains two independent arbitrary constants.
- Option D) 0
- Incorrect because the solution still contains arbitrary constants and therefore represents a differential equation of positive order.
Used
- Identify Independent Arbitrary Constants
Application:
- Combine like terms involving the same function.
- Count only the independent arbitrary constants.
Final Logic:
- Since
- \(c_{1}e^{x}+c_{3}e^{x}=(c_{1}+c_{3})e^{x},\)
- only two independent constants remain.
- Therefore, the differential equation is of order 2, making Option B correct.
Repeated functions share one arbitrary constant.
2 Match the multi-parameter function to the order of its corresponding differential equation.
| List I | List II |
|---|---|
| 1. y = a sin(x+b) | a. Differentiate once, substitute to get x + y y' = 0 |
| 2. x² + y² = a² | b. Differentiate twice, yielding y'' + y = 0 |
| 3. y = mx | c. Differentiate twice, eliminate parameters to get x y y'' + x(y')² - y y' = 0 |
| 4. x²/a² + y²/b² = 1 | d. Differentiate once, substitute y/x for parameter |
Parameters determine order Geometry links to DE order Standard classification used
(1) a sin(x+b) → 2 parameters → order c mapping (2) circle → single differentiation → order a (3) exponential form → order b reduction (4) 4 parameters → highest order (d)
- A → inconsistent ordering
- B → swaps geometry mapping
- C → misclassifies circle structure
Option grouping
- match parameter count with order
"More parameters → higher order"
3 In solving the equation
(x+1)dy/dx=2xy
with the initial condition
y(2)=3,
which sequential steps are mathematically correct?
Statements:
A. The separated form is
dy/y=2x/(x+1) " " dx.
B. Integration yields
log∣y∣=2x-2log∣x+1∣+c.
C. The integration requires writing
2x/(x+1)=2-2/(x+1).
D. The constant cevaluates to
log3-4+2log3.
Separate the variables, simplify the integrand using algebraic manipulation, integrate both sides, and finally apply the initial condition \(y(2)=3\) to determine the constant.
Given, \((x+1)\frac{dy}{dx}=2xy.\) Step 1: Separate the variables \(\frac{dy}{y}=\frac{2x}{x+1} dx.\) Hence, Statement A is correct. Step 2: Simplify the integrand Rewrite \(\frac{2x}{x+1}=2-\frac{2}{x+1}.\) This makes the integration straightforward. Hence, Statement C is correct. Step 3: Integrate both sides \(\int \frac{dy}{y}=\int \left(2,\ \frac{2}{x+1}\right)dx.\) Therefore, \(log∣y∣=2x-2log∣x+1∣+c.\) Hence, Statement B is correct. Step 4: Apply the initial condition Using \(x=2,y=3,log3=4-2log3+c.\) Thus, \(c=log3-4+2log3.\) Hence, Statement D is also correct. Therefore, all four statements are correct. Answer: Option D
- Option A (A, B, D) – Incorrect because Statement C is also correct and is an essential algebraic step before integration.
- Option B (A, B) – Incorrect because Statements C and D are both correct.
- Option C (A, B, C) – Incorrect because Statement D correctly evaluates the constant using the initial condition.
- Option D (A, B, C, D) – Correct because all four statements are mathematically valid.
Used
- Variable Separation + Algebraic Simplification + Initial Condition
Application:
- 1. Separate the variables.
- 2. Simplify the rational expression.
- 3. Integrate both sides.
- 4. Apply the given initial condition to determine the arbitrary constant.
Substitute the initial condition.
4 Identify the INCORRECT statement regarding the particular solution of
dy/dx=x(2logx+1)
with the initial condition
y(2)=0.
The integral \(\int xlogx dx\) is evaluated using integration by parts because it is the product of two functions. The expression \(\frac{1}{x}\) is the derivative of \(\log\,x\), not its integral.
Given, \(\frac{dy}{dx}=x(2logx+1).\) Integrate both sides: \(y=\int x(2logx+1) dx.\) Expanding, \(y=2\int xlogx dx+\int x dx.\) Evaluate \(\int xlogx dx\) using integration by parts. Let \(u=logx,dv=x dx.\) Then, \(du=\frac{1}{x} dx,v=\frac{x^{2}}{2}.\) Applying integration by parts, \(\int xlogx dx=\frac{x^{2}}{2}logx-\frac{x^{2}}{4}.\) Therefore, \(y=x^{2}logx+c.\) Using the initial condition \(y(2)=0,0=4log2+c.\) Hence, \(c=-4log2.\) Therefore, Statements A, B, and C are correct. Statement D is incorrect because \(\frac{d}{dx}(logx)=\frac{1}{x},\) but \(\int logx dx\neq \frac{1}{x}.\) Hence, Option D is the incorrect statement.
- Option A
- Correct.
- The integral
- \(\int xlogx dx\)
- is a product of two functions and requires integration by parts.
- Option B
- Correct.
- Integrating
- \(x(2logx+1)\)
- gives
- \(y=x^{2}logx+c.\)
- Option C
- Correct.
- Substituting
- \(x=2, y=0\)
- into
- \(y=x^{2}logx+c\)
- gives
- \(0=4log2+c,\)
- so
- \(c=-4log2.\)
- Option D
- Incorrect.
- The expression
- \(\frac{1}{x}\)
- is the derivative of
- \(logx,\)
- not its integral.
- Therefore,
- \(\int xlogx dx\)
- must be evaluated using integration by parts, not by directly integrating \(\log\,x\) as \(1/x\).
Used
- Integration by Parts
- Steps:
- 1. Expand the integrand.
- 2. Apply integration by parts to
- \(\int xlogx dx.\)
- 1. Integrate the remaining term directly.
- 2. Use the initial condition to determine the arbitrary constant.
Do not confuse differentiation with integration.
5 A mixture of parabolas with vertices at the origin and foci on the positive y-axis is represented by
x^2=4ay.
The differential equation for this family of integral curves is:
Differentiate the given family of curves with respect to \(x\), then eliminate the arbitrary constant \(a\) using the original equation to obtain the required differential equation.
Given the family of curves, \(x^{2}=4ay.\) Differentiate both sides with respect to \(x\): \(2x=4a\frac{dy}{dx}.\) From the original equation, \(4a=\frac{x^{2}}{y}.\) Substitute this into the differentiated equation: \(2x=\frac{x^{2}}{y}\frac{dy}{dx}.\) Multiply both sides by \(y\): \(2xy=x^{2}\frac{dy}{dx}.\) Divide both sides by \(x\left(x,\ 0\right)\): \(2y=x\frac{dy}{dx}.\) Therefore, \(x\frac{dy}{dx}=2y.\) Hence, Option B is correct.
- Option A)
- \(2x=4a\frac{dy}{dx}\)
- Incorrect because this is only the intermediate differentiated equation.
- The arbitrary constant \(a\) has not been eliminated, so it is not the required differential equation.
- Option C)
- \(y\frac{dy}{dx}=2x\)
- Incorrect because the variables are arranged incorrectly after eliminating \(a\).
- Option D)
- \(\frac{dy}{dx}=x^{2}\)
- Incorrect because it bears no relation to the differentiated form of
- \(x^{2}=4ay.\)
Used
- Formation of Differential Equation by Eliminating the Arbitrary Constant
- Steps:
- 1. Differentiate the given family of curves.
- 2. Express the arbitrary constant from the original equation.
- 3. Substitute it into the differentiated equation.
- 4. Simplify to eliminate the arbitrary constant completely.
Simplify to obtain the differential equation.
6 Graphically, forming the differential equation for circles having their center on the y-axis and passing through the origin requires establishing the equation
\(x^{2}+(y-a)^{2}=a^{2}.\)
What is the geometric constraint applied when differentiating?
While forming a differential equation, the arbitrary constant 'a' is eliminated after differentiation. Since there is only one arbitrary constant, the resulting differential equation is of the first order.
The given family of circles is \(x^{2}+(y-a)^{2}=a^{2}.\) Here, \(a\) is the only arbitrary constant representing the y-coordinate of the centre. To form the differential equation: 1. Differentiate the given equation with respect to \(x\). 2. Use the original equation and the differentiated equation together. 3. Eliminate the arbitrary constant \(a\). The objective is not to remove \(a\) because it is fixed, but because differential equations are formed by eliminating arbitrary constants from the given family of curves. Hence, Option B is correct.
- Option A)
- Incorrect because 'a' is not a fixed constant.
- It is an arbitrary constant whose value varies from one circle to another and must be eliminated.
- Option C)
- Incorrect because there is no condition stating that the x-intercept equals 'a'.
- The parameter 'a' specifies the centre of the circle on the y-axis.
- Option D)
- Incorrect because the circles have a finite radius equal to a.
- Infinite radius would correspond to a straight line, not a circle.
Used
- Formation of Differential Equations by Eliminating Arbitrary Constants
Application:
- Identify the arbitrary constant in the family of curves.
- Differentiate the equation.
- Eliminate the arbitrary constant using the original and differentiated equations.
Final Logic:
- Since 'a' is the only arbitrary parameter, it is eliminated to obtain the required differential equation.
- Therefore, Option B is correct.
Always eliminate the arbitrary constant(s), not fixed numerical values.
7 Sequentially verifying
y=2e^2x-3e^(-x)
for the equation
(d^2 y)/(dx^2 )-dy/dx=2y
requires finding the second derivative. What is
(d^2 y)/(dx^2 )?
Differentiate the given function twice. Apply the chain rule while differentiating exponential functions.
Given, \(y=2e^{2x}-3e^{-x}.\) Step 1: Find the first derivative Differentiate term by term: \(\frac{dy}{dx}=2\left(2e^{2x}\right)-3\left(,\ e^{-x}\right)\frac{dy}{dx}=4e^{2x}+3e^{-x}.\) Step 2: Find the second derivative Differentiate again: \(\frac{d^{2}y}{dx^{2}}=4\left(2e^{2x}\right)+3\left(,\ e^{-x}\right)\frac{d^{2}y}{dx^{2}}=8e^{2x}-3e^{-x}.\) Hence, Option B is correct
- Option A)
- \(4e^{2x}+3e^{-x}\)
- Incorrect because this is the first derivative, not the second derivative.
- Option C)
- \(4e^{2x}-3e^{-x}\)
- Incorrect because the derivative of
- \(4e^{2x}\)
- is
- \(8e^{2x},\)
- not
- \(4e^{2x}.\)
- Option D)
- \(2e^{2x}+3e^{-x}\)
- Incorrect because neither exponential term has been differentiated correctly.
Used
- Successive Differentiation (Chain Rule)
Application:
- Differentiate the function once to obtain
- \(\frac{dy}{dx}.\)
- Differentiate again to obtain
- \(\frac{d^{2}y}{dx^{2}}.\)
Final Logic:
- Since
- \(\frac{d}{dx}\left(e^{2x}\right)=2e^{2x}\)
- and
- \(\frac{d}{dx}\left(e^{-x}\right)=-e^{-x},\)
- the second derivative is
- \(\frac{d^{2}y}{dx^{2}}=8e^{2x}-3e^{-x}.\)
- Therefore, Option B is correct.
Differentiate again for \(d^{2}y/dx^{2}\).
8 Verifying
y=a+logx
for the equation
x (d^2 y)/(dx^2 )+dy/dx=0
involves tracking the derivatives. The second derivative
(d^2 y)/(dx^2 )
evaluates to:
Differentiate the given function twice. The constant a disappears after differentiation, and the derivative of 1/x gives −1/x².
Given, \(y=a+logx.\) Step 1: Find the first derivative Since a is a constant, \(\frac{d}{dx}(a)=0.\) Also, \(\frac{d}{dx}(logx)=\frac{1}{x}.\) Therefore, \(\frac{dy}{dx}=\frac{1}{x}.\) Step 2: Find the second derivative Differentiate again: \(\frac{d^{2}y}{dx^{2}}=\frac{d}{dx}\left(\frac{1}{x}\right)=\frac{d}{dx}(x^{-1})=-x^{-2}.\) Hence, \(\frac{d^{2}y}{dx^{2}}=-\frac{1}{x^{2}}.\) Therefore, Option B is correct.
- Option A)
- \(\frac{1}{x}\)
- Incorrect because this is the first derivative, not the second derivative.
- Option C)
- \(\frac{1}{x^{2}}\)
- Incorrect because the negative sign has been omitted.
- Option D)
- \(-\frac{1}{x^{3}}\)
- Incorrect because differentiating
- \(\frac{1}{x}\)
- gives
- \(-\frac{1}{x^{2}},\)
- not
- \(-\frac{1}{x^{3}}.\)
Used
- Successive Differentiation
Application:
- 1. Differentiate the given function once to obtain
- \(\frac{dy}{dx}.\)
- 1. Differentiate again to obtain
- \(\frac{d^{2}y}{dx^{2}}.\)
- 1. Substitute the derivatives into the differential equation for verification.
\(logx ⟶ \frac{1}{x} ⟶ -\frac{1}{x^{2}}\)
9 What is the probability that implicitly differentiating
(x^2-y^2)dy/dx-2xy=0
is required to verify the family of circles passing through the origin with centre on the x-axis?
The given expression is already a differential equation obtained through implicit differentiation. Therefore, verifying the family of circles necessarily requires implicit differentiation, making the probability equal to 1 (certainty).
The family of circles with centre on the x-axis and passing through the origin is represented by \(\left(x-a)^{2}+y^{2}=a^{2}.\right.\) To obtain or verify the corresponding differential equation: 1. Differentiate the equation implicitly with respect to \(x\). 2. Eliminate the arbitrary constant \(a\). 3. Simplify the result to obtain \((x^{2}-y^{2})\frac{dy}{dx}-2xy=0.\) Since every verification of this family requires implicit differentiation, the event is certain. Therefore, \(P(Implicit differentiation is required)=1.\) Hence, Option D is correct.
- Option A)
- \(0\)
- Incorrect because implicit differentiation is definitely required.
- Option B)
- \(0.5\)
- Incorrect because the event is not equally likely; it is certain.
- Option C)
- \(0.75\)
- Incorrect because there is no uncertainty involved.
- Option D)
- \(1\)
- Correct because the probability of a certain event is 1.
Used
- Formation and Verification of Differential Equations
Application:
- Identify the family of curves.
- Differentiate the equation implicitly.
- Eliminate the arbitrary constant.
- Verify the resulting differential equation.
- Since implicit differentiation is unavoidable, the probability is 1.
If a mathematical step is always required, its probability is 1.
10 To verify that
x(y (d^2 y)/(dx^2 )ⓜ+(dy/dx)^2 )=y dy/dx
derives from
x^2/a^2 +y^2/b^2 =1,
we differentiate implicitly twice. After the first differentiation, we get
x/a^2 +(y dy/dx)/b^2 =0.
The next crucial vector-like substitution step is:
After the first differentiation, rearrange the equation to express the ratio involving the arbitrary constants. This allows the constants \(a\) and \(b\) to be eliminated after the second differentiation.
Given, \(\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1.\) Step 1: Differentiate implicitly \(\frac{2x}{a^{2}}+\frac{2y}{b^{2}}\frac{dy}{dx}=0.\) Dividing by 2, \(\frac{x}{a^{2}}+\frac{y\frac{dy}{dx}}{b^{2}}=0.\) Step 2: Rearrange Move one term to the other side: \(\frac{x}{a^{2}}=-\frac{y\frac{dy}{dx}}{b^{2}}.\) Hence, \(\frac{yy_{1}}{x}=-\frac{b^{2}}{a^{2}},\) where \(y_{1}=\frac{dy}{dx}.\) The right-hand side now consists only of constants. Step 3: Differentiate again Differentiate \(\frac{yy_{1}}{x}=-\frac{b^{2}}{a^{2}}\) with respect to \(x\). Since the right-hand side is constant, its derivative is zero. This eliminates the arbitrary constants completely and leads to \(x\left(y\frac{d^{2}y}{dx^{2}},\ {\left(\frac{dy}{dx}\right)}^{2}\right)=y\frac{dy}{dx}.\) Therefore, Option B is correct.
- Option A)
- Incorrect because merely multiplying by
- \(a^{2}\)
- does not eliminate both arbitrary constants.
- Option C)
- Incorrect because the problem requires differentiation, not integration.
- Option D)
- Incorrect because there is no justification for assuming
- \(y_{1}=\frac{dy}{dx}=0.\)
Used
- Implicit Differentiation and Elimination of Arbitrary Constants
Application:
- 1. Differentiate the family of curves.
- 2. Rearrange to isolate the ratio containing constants.
- 3. Differentiate again.
- 4. Eliminate the arbitrary constants to obtain the differential equation.
Always eliminate the constants after differentiation.
11 To find the bounding function y(x)when
dy/dx=e^x.e^y+x^2 e^y,
factoring out e^ygives
dy/dx=e^y (e^x+x^2).
The separated integrable area form is:
Factor out \(e^{y}\)from the right-hand side and divide both sides by \(e^{y}\). This separates all \(y\)-terms on one side and all \(x\)-terms on the other.
Given, \(\frac{dy}{dx}=e^{x}.e^{y}+x^{2}e^{y}.\) Factor out \(e^{y}\): \(\frac{dy}{dx}=e^{y}(e^{x}+x^{2}).\) Now divide both sides by \(e^{y}\): \(e^{-y}\frac{dy}{dx}=e^{x}+x^{2}.\) Multiply both sides by \(dx\): \(e^{-y} dy=(e^{x}+x^{2}) dx.\) This successfully separates the variables, making the equation ready for integration. Hence, Option B is correct.
- Option A)
- \(e^{y} dy=(e^{x}+x^{2}) dx\)
- Incorrect because the equation requires dividing by \(e^{y}\), giving \(e^{-y}\), not multiplying by \(e^{y}\).
- Option C)
- \(dy=e^{y}(e^{x}+x^{2}) dx\)
- Incorrect because this is merely the original equation written in differential form.
- The variables are not separated.
- Option D)
- \(e^{-x} dy=e^{y}x^{2} dx\)
- Incorrect because \(e^{-x}\)does not arise from separating the given differential equation.
- The algebraic manipulation is invalid.
Used
- Variable Separation
Application:
- 1. Factor out the common term \(e^{y}\).
- 2. Divide both sides by \(e^{y}\).
- 3. Multiply by \(dx\).
- 4. Arrange all \(y\)-terms on the left and all \(x\)-terms on the right before integrating.
Keep all \(y\)-terms on the left and \(x\)-terms on the right.
12 Integrating the separated form
y/(y+2) " " dy=(x+2)/x " " dx
obtained from the differential equation
xy dy/dx=(x+2)(y+2),
yields:
Rewrite both rational expressions into simpler forms, integrate each side separately, and combine the constants to obtain the general solution.
Given, \(\frac{y}{y+2} dy=\frac{x+2}{x} dx.\) Step 1: Simplify both sides Write \(\frac{y}{y+2}=1-\frac{2}{y+2}\) and \(\frac{x+2}{x}=1+\frac{2}{x}.\) Step 2: Integrate both sides \(\int \left(1,\ \frac{2}{y+2}\right)dy=\int \left(1,\ \frac{2}{x}\right)dx.\) Integrating, \(y-2log∣y+2∣=x+2log∣x∣+c.\) Hence, Option A is correct.
- Option A)
- Correct.
- Both rational expressions are simplified correctly before integration.
- Option B)
- \(y+2log∣y+2∣=x+2log∣x∣+c\)
- Incorrect because
- \(\int -\frac{2}{y+2} dy=-2log∣y+2∣,\)
- not
- \(+2log∣y+2∣.\)
- Option C)
- \(log∣y∣=log∣x+2∣+c\)
- Incorrect because neither side integrates to these logarithmic expressions.
- Option D)
- \(\frac{y^{2}}{2}=\frac{x^{2}}{2}+2x+c\)
- Incorrect because this would result from integrating y and x+2 directly, without simplifying the given rational expressions.
Used
- Algebraic Simplification + Variable Separation + Direct Integration
Application:
- 1. Separate the variables.
- 2. Rewrite rational expressions:
- \(\frac{y}{y+2}=1-\frac{2}{y+2},\frac{x+2}{x}=1+\frac{2}{x}.\)
- 1. Integrate each term separately.
- 2. Combine the integration constants.
This makes the integration straightforward.
13 13. Algebraically separate the variables for \(x(e^{2y}-1) dy+(x^{2}-1)e^{y} dx=0\):
Move one differential term to the opposite side. Divide by common factors. Collect all \(y\)-terms and \(dy\) together, \(x\)-terms and \(dx\) together.
Given, \(x(e^{2y}-1) dy+(x^{2}-1)e^{y} dx=0.\) Move the second term to the right-hand side: \(x(e^{2y}-1) dy=-(x^{2}-1)e^{y} dx.\) Since \(-(x^{2}-1)=1-x^{2},\) we have \(x(e^{2y}-1) dy=(1-x^{2})e^{y} dx.\) Now divide both sides by \(xe^{y}.\) This gives \(\frac{e^{2y}-1}{e^{y}} dy=\frac{1-x^{2}}{x} dx.\) Thus, the variables are completely separated. Hence, Option A is correct.
- Option A)
- Correct.
- The variables are completely separated with all \(y\)-terms on the left and all \(x\)-terms on the right.
- Option B)
- \(x(e^{2y}-1) dy=(x^{2}-1)e^{y} dx\)
- Incorrect because the negative sign is omitted after transposing the term.
- The variables are also not separated.
- Option C)
- \(e^{y} dy=x dx\)
- Incorrect because it ignores the factors
- \(e^{2y}-1\)
- and
- \(x^{2}-1.\)
- Option D)
- \(\frac{e^{2y}-1}{x} dy=\frac{x^{2}-1}{e^{y}} dx\)
- Incorrect because the division is performed incorrectly.
- The left-hand side still contains an \(x\)-term and the right-hand side still contains a \(y\)-term, so the variables are not separated.
Used
- Variable Separation
Application:
- 1. Move one differential term to the opposite side.
- 2. Divide by the common factors involving both variables.
- 3. Arrange all \(y\)-terms on one side and all \(x\)-terms on the other.
- 4. The resulting equation is ready for integration.
Keep all \(y\)-terms on the left and all \(x\)-terms on the right.
14 After separating
(e^2y-1)/e^y " " dy=(1-x^2)/x " " dx
into
(e^y-e^(-y))" " dy=(1/xⓜ-x)" " dx,
integrating both sides yields:
Rewrite the equation in an integrable form and integrate each term separately using standard exponential and logarithmic integration formulas.
Given, \((e^{y}-e^{-y}) dy=\left(\frac{1}{x},\ x\right) dx.\) Integrate both sides: \(\int (e^{y}-e^{-y}) dy=\int \left(\frac{1}{x},\ x\right) dx.\) Left-hand side Using standard integrals, \(\int e^{y} dy=e^{y}\) and \(\int (-e^{-y}) dy=e^{-y}.\) Therefore, \(\int (e^{y}-e^{-y}) dy=e^{y}+e^{-y}.\) Right-hand side Using standard integrals, \(\int \frac{1}{x} dx=log∣x∣\) and \(\int (-x) dx=-\frac{x^{2}}{2}.\) Hence, \(\int \left(\frac{1}{x},\ x\right) dx=log∣x∣-\frac{x^{2}}{2}+c.\) Therefore, \(e^{y}+e^{-y}=log∣x∣-\frac{x^{2}}{2}+c.\) Hence, Option A is correct.
- Option A)
- Correct.
- Both sides are integrated correctly using standard integration formulas.
- Option B)
- \(e^{y}-e^{-y}=log∣x∣+\frac{x^{2}}{2}+c\)
- Incorrect because
- \(\int (-e^{-y}) dy=e^{-y}\), not \(-e^{-y}\).
- \(\int (-x) dx=-\frac{x^{2}}{2}\), not \(+\frac{x^{2}}{2}\).
- Option C)
- \(\frac{e^{2y}}{2}=log∣x∣-x+c\)
- Incorrect because \(e^{y}-e^{-y}\)is not integrated as \(\frac{e^{2y}}{2}\).
- Option D)
- \(e^{y}+e^{-y}=\frac{1}{x^{2}}-\frac{x^{2}}{2}+c\)
- Incorrect because
- \(\int \frac{1}{x} dx=log∣x∣,\)
- not
- \(\frac{1}{x^{2}}.\)
Used
- Variable Separation + Direct Integration
Application:
- 1. Simplify the separated equation.
- 2. Integrate exponential terms on the left.
- 3. Integrate logarithmic and polynomial terms on the right.
- 4. Combine the integration constant.
\(\int x dx=\frac{x^{2}}{2}+C\)
15 Rearranging the complex equation
log(dy/dx)=3x+4y
to solve it requires which initial algebraic manipulation?
Since the differential equation is expressed in logarithmic form, the first step is to remove the logarithm by converting it into its equivalent exponential form.
Given, \(log\left(\frac{dy}{dx}\right)=3x+4y.\) Using the logarithmic identity \(logA=B⟺A=e^{B},\) we obtain \(\frac{dy}{dx}=e^{3x+4y}.\) Further, \(e^{3x+4y}=e^{3x}e^{4y},\) which can then be separated as \(e^{-4y} dy=e^{3x} dx.\) Thus, the initial algebraic manipulation is converting the logarithmic equation into its exponential form. Hence, Option B is correct.
- Option A)
- Incorrect because differentiation is not the first step.
- The logarithm must first be removed by converting to exponential form.
- Option B)
- Correct.
- Applying
- \(logA=B⟹A=e^{B}\)
- gives
- \(\frac{dy}{dx}=e^{3x+4y}.\)
- Option C)
- Incorrect because there is no mathematical basis for dividing both sides by \(3x\).
- Option D)
- Incorrect because \(4y\) is already part of the exponent after conversion.
- Taking another logarithm is unnecessary and incorrect.
Used
- Logarithmic to Exponential Conversion
Application:
- 1. Identify the logarithmic equation.
- 2. Apply the identity
- \(logA=B⟺A=e^{B}.\)
- 1. Rewrite the differential equation.
- 2. Proceed with variable separation if required.
Convert logarithmic equations to exponential form before attempting differentiation or separation of variables.
16 When evaluating the integrated exponential form
e^(-4y)/(-4)=e^3x/3+c,
multiplying by −12 to clear fractions changes the arbitrary constant cto −12c. By convention, this is usually rewritten as:
Multiplying an arbitrary constant by any non-zero constant still produces another arbitrary constant. Hence, −12c is simply renamed as a new arbitrary constant, usually denoted by \(C\) or \(C_{1}\).
Given, \(\frac{e^{-4y}}{-4}=\frac{e^{3x}}{3}+c.\) Multiply both sides by −12: \(3e^{-4y}=-4e^{3x}-12c.\) Since \(c\) is an arbitrary constant, \(-12c\) is also an arbitrary constant. Therefore, instead of writing −12c, we simply write \(C\) (or \(C_{1}\)). Thus, the equation becomes \(3e^{-4y}=-4e^{3x}+C.\) This is standard practice in solving differential equations. Hence, Option B is correct.
- Option A)
- \(Ke^{x}\)
- Incorrect because multiplying an arbitrary constant by −12 does not introduce an exponential factor.
- The constant remains an arbitrary constant.
- Option B)
- Correct.
- Any non-zero multiple of an arbitrary constant is itself another arbitrary constant and is conventionally denoted by \(C\) or \(C_{1}\).
- Option C)
- Incorrect because arbitrary constants do not cancel when multiplied by a non-zero number.
- Option D)
- Incorrect because multiplying by a constant does not convert it into a logarithmic term.
Used
- Properties of Arbitrary Constants
Application:
- 1. Multiply both sides of the equation to eliminate fractions.
- 2. Recognize that a non-zero multiple of an arbitrary constant is still arbitrary.
- 3. Replace the transformed constant with a new arbitrary constant.
Final Logic:
- Since
- \(-12c\)
- is still arbitrary, it is rewritten as
- \(C.\)
- Therefore, Option B is correct.
After algebraic simplification, simply replace them with a new constant \(C\).
17 The general solution to
log(dy/dx)=3x+4y
after complete integration and rearrangement is:
Convert the logarithmic equation into exponential form, separate the variables, integrate both sides, and combine the constants to obtain the general solution.
Given, \(log\left(\frac{dy}{dx}\right)=3x+4y.\) Step 1: Convert to exponential form Using \(logA=B⟹A=e^{B},\) we obtain \(\frac{dy}{dx}=e^{3x+4y}=e^{3x}e^{4y}.\) Step 2: Separate the variables \(e^{-4y} dy=e^{3x} dx.\) Step 3: Integrate both sides \(\int e^{-4y} dy=\int e^{3x} dx.\) This gives \(-\frac{e^{-4y}}{4}=\frac{e^{3x}}{3}+c.\) Step 4: Eliminate the fractions Multiply both sides by −12: \(3e^{-4y}=-4e^{3x}+C.\) Rearranging, \(3e^{-4y}+4e^{3x}=C.\) Hence, Option A is correct.
- Option A)
- \(3e^{-4y}+4e^{3x}=C\)
- Correct.
- This is the correctly rearranged general solution after integration.
- Option B)
- \(4e^{-4y}+3e^{3x}=C\)
- Incorrect because the coefficients are interchanged.
- Integration gives coefficients 3 and 4 in the opposite positions.
- Option C)
- \(e^{3x}+e^{4y}=C\)
- Incorrect because the integral of
- \(e^{-4y}\)
- is not
- \(e^{4y}.\)
- Option D)
- \(-4e^{3x}+3e^{-4y}=C\)
- Incorrect because this is not the standard rearranged form after combining the constants.
- The accepted form places both exponential terms on the left-hand side.
Used
- Logarithmic Transformation + Variable Separation + Direct Integration
Application:
- 1. Convert the logarithmic equation into exponential form.
- 2. Separate the variables.
- 3. Integrate both sides.
- 4. Remove fractions by multiplying through by the LCM.
- 5. Rearrange the equation into its standard general solution.
Rearrange to the final general solution.
18 For the differential equation
dy/dx=(x+1)/(2-y),
the functional relationship defining the general solution curve family is analytically given by:
Separate the variables, integrate both sides, and combine the resulting expressions into a single constant to obtain the general solution.
Given, \(\frac{dy}{dx}=\frac{x+1}{2-y}.\) Step 1: Separate the variables \((2-y) dy=(x+1) dx.\) Step 2: Integrate both sides \(\int (2-y) dy=\int (x+1) dx.\) Evaluating the integrals, \(2y-\frac{y^{2}}{2}=\frac{x^{2}}{2}+x+c.\) Step 3: Remove the fraction Multiply both sides by 2: \(4y-y^{2}=x^{2}+2x+C.\) Rearranging, \(y^{2}-4y+x^{2}+2x=C.\) Hence, Option A is correct.
- Option A)
- \(y^{2}-4y+x^{2}+2x=C\)
- Correct.
- This is the general solution obtained after separating variables and integrating.
- Option B)
- \(y^{2}+2y-x^{2}=C\)
- Incorrect because the integration of
- \(2-y\)
- does not produce the term
- \(y^{2}+2y.\)
- Option C)
- \(e^{y}=x^{2}+C\)
- Incorrect because no exponential function appears during integration.
- Option D)
- \(y=log(x+1)+C\)
- Incorrect because neither side involves the integral
- \(\int \frac{1}{x+1} dx.\)
Used
- Variable Separation + Direct Integration
Application:
- 1. Separate the variables.
- 2. Integrate each side independently.
- 3. Remove fractional coefficients.
- 4. Rearrange into the standard implicit form of the general solution.
Clear fractions before writing the final answer.
19
xy dy/dx=(x+2)(y+2).
Separating the variables gives
y/(y+2) " " dy=(x+2)/x " " dx.
Rewrite the fractions as
(1ⓜ-2/(y+2))dy=(1ⓜ+2/x)dx.
Integrating both sides,
y-2log∣y+2∣=x+2log∣x∣+c.
If the required curve passes through the point
(1,-1),
substitute these coordinates into the general solution to determine the value of the arbitrary constant. Substituting this value back into the general solution gives the required particular solution.
x=1,y=-1
into
y-2log∣y+2∣=x+2log∣x∣+c
yields what exact value for c?
Substitute the coordinates \(\left(1,-1\right)\)into the general solution and solve for the arbitrary constant.
The general solution is \(y-2log∣y+2∣=x+2log∣x∣+c.\) Substitute \(x=1,y=-1.\) Then, \(-1-2log1=1+2log1+c.\) Since \(log1=0,\) we get \(-1=1+c.\) Therefore, \(c=-2.\) Hence, Option B is correct.
- Option A)
- \(c=0\)
- Incorrect because substitution gives
- \(c=-2.\)
- Option C)
- \(c=1\)
- Incorrect because it does not satisfy the given point.
- Option D)
- \(c=2\)
- Incorrect because substituting the point yields
- \(c=-2,\)
- not \(2\).
Used
- Finding the Arbitrary Constant Using a Given Point
Application:
- Write the general solution.
- Substitute the given coordinates.
- Use
- \(log1=0\)
- to simplify.
- Solve for the arbitrary constant.
Determine the constant.
20
xy dy/dx=(x+2)(y+2).
Separating the variables gives
y/(y+2) " " dy=(x+2)/x " " dx.
Rewrite the fractions as
(1ⓜ-2/(y+2))dy=(1ⓜ+2/x)dx.
Integrating both sides,
y-2log∣y+2∣=x+2log∣x∣+c.
If the required curve passes through the point
(1,-1),
substitute these coordinates into the general solution to determine the value of the arbitrary constant. Substituting this value back into the general solution gives the required particular solution.
\(c=-2,\)
the final particular solution algebraically simplifies to:
Substitute the value of the arbitrary constant into the general solution and combine the logarithmic terms using logarithmic identities.
The general solution is \(y-2log∣y+2∣=x+2log∣x∣+c.\) Substituting \(c=-2,\) gives \(y-2log∣y+2∣=x+2log∣x∣-2.\) Rearranging, \(y-x+2=2log∣x∣+2log∣y+2∣.\) Using the logarithmic identity \(loga+logb=log(ab),\) we obtain \(2log∣x(y+2)∣.\) Hence, \(y-x+2=2log∣x(y+2)∣.\) Therefore, Option A is correct.
- Option A)
- Correct.
- It is obtained by substituting
- \(c=-2\)
- and combining logarithms correctly.
- Option B)
- Incorrect because the logarithmic terms are not combined correctly and the algebraic rearrangement is incorrect.
- Option C)
- Incorrect because it omits the term
- \(2log∣y+2∣\)
- and the constant adjustment.
- Option D)
- Incorrect because the coefficient 2 of the logarithm has been omitted.
Used
- Substitution + Logarithmic Properties
Application:
- 1. Substitute the value of the arbitrary constant.
- 2. Rearrange the equation.
- 3. Use
- \(2log∣a∣+2log∣b∣=2log∣ab∣.\)
- 1. Write the particular solution in its simplified form.
This helps simplify the final particular solution.
