UG Mathematics Booster Test 2 - Continuity Fundamentals
π Answers are locked once submitted β results and explanations appear at the end.
QUESTION 1 OF 20
As xβa, the values of a function f(x) form sequences tending to L.
For the function to be continuous at x=a, what must hold?
QUESTION 2 OF 20
For the function
\(f(x)=\frac{1}{x}\)
as xβ0^+, the graph approaches +β.
This implies:
QUESTION 3 OF 20
Let
\(f(x)=\left\{\begin{pmatrix}x+4, & x<3\\ 2x, & x\geq 3\end{pmatrix}\right.\)
Find the left-hand limit at x=3.
QUESTION 4 OF 20
Let a velocity component be defined as:
\(v(t)=\left\{\begin{pmatrix}t^{2}, & t<2\\ kt, & t\geq 2\end{pmatrix}\right.\)
For continuity at t=2, the right-hand limit must equal:
QUESTION 5 OF 20
To compute the area under a curve \(y=f(x)\)on [a,b], which condition ensures integrability via continuity?
QUESTION 6 OF 20
Let
\(f(x)=\left\{\begin{pmatrix}x^{2}, & x\neq 1\\ 3, & x=1\end{pmatrix}\right.\)
Here,
\({limβ‘}_{x\rightarrow 1}f(x)=1\neq f(1)\)
This implies:
QUESTION 7 OF 20
Assertion (A):
The function
\(f(x)=\left\{\begin{pmatrix}-1, & x<0\\ 1, & x\geq 0\end{pmatrix}\right.\)
is continuous at x=0.
Reason (R):
The LHL at x=0 is β1 and the RHL is 1; since LHL β RHL, the limit does not exist.
QUESTION 8 OF 20
Arrange steps to check continuity of f(x) at x=a:
1. Compute \({limβ‘}_{x\rightarrow a}f(x)\)
2. Check if \({limβ‘}_{x\rightarrow a}f(x)=f(a)\)
3. Evaluate f(a)
4. Conclude continuity
QUESTION 9 OF 20
Match each function with the reason for discontinuity at x=0:
| List I | List II |
|---|---|
| 1. \(f(x)=1/x\) | a. LHL β RHL (jump discontinuity) |
| 2. \(f(x)=\left\{\begin{pmatrix}1, & x<0\\ 2, & x>0\end{pmatrix}\right.\) | b. Limit exists but β f(0) (removable) |
| 3. \(f(x)=\left\{\begin{pmatrix}x, & x\neq 0\\ 5, & x=0\end{pmatrix}\right.\) | c. Limit undefined (infinite discontinuity) |
| 4. \(f(x)=βxβ\) | d. Step/jump behavior (e.g., β1 to 0) |
QUESTION 10 OF 20
Which of the following functions have exactly one point of discontinuity?
i. \(f(x)=1/x\)
ii. \(f(x)=\left\{\begin{pmatrix}1, & x\neq 2\\ 5, & x=2\end{pmatrix}\right.\)
iii. \(f(x)=β£xβ£\)
QUESTION 11 OF 20
Identify the INCORRECT statement:
QUESTION 12 OF 20
A function has a jump discontinuity at x=a.
If LHL = 5 and RHL = 12, what is the magnitude of the jump?
QUESTION 13 OF 20
If f(x) and g(x) are continuous functions, which is guaranteed to be continuous wherever defined?
QUESTION 14 OF 20
Why is the function \(f(x)=β£x^{2}-1β£\)continuous?
QUESTION 15 OF 20
Let \(f(x)=k\) be constant. If \(f(3)=10\), find k.
QUESTION 16 OF 20
For \(f(x)=x\), evaluate:
\({limβ‘}_{x\rightarrow a}f(x)\)
QUESTION 17 OF 20
Which function is continuous for all real x?
QUESTION 18 OF 20
If a function is defined only at x=5, it is:
QUESTION 19 OF 20
For continuity on [a,b], which is NOT required?
QUESTION 20 OF 20
For a function on [-2,2], continuity at x=2 requires checking:
Test Complete!
Answer Review
1 As xβa, the values of a function f(x) form sequences tending to L.
For the function to be continuous at x=a, what must hold?
Continuity links limit and function value Limit near a must equal actual value Defined equality condition is necessary
For continuity at x=a, \({limβ‘}_{x\rightarrow a}f(x)=f(a)\) If nearby function values approach L, then continuity requires f(a)=L. Hence option B is correct. Option A is unrelated. Option C is impossible for finite continuity. Option D violates the requirement that the function must be defined at x=a.
- Option A β Continuity does not require the function value to be zero unless the limit itself is zero.
- Option C β Infinite values do not satisfy ordinary continuity conditions for real-valued functions.
- Option D β An undefined function value makes continuity impossible at that point.
Used: Contextual/Tonal Matching
Application:
- Match the statement directly with the formal continuity definition.
Final Logic:
- Continuity means function value equals the approaching limit.
"Continuous = Limit equals value"
2 For the function
\(f(x)=\frac{1}{x}\)
as xβ0^+, the graph approaches +β.
This implies:
Reciprocal grows unbounded near zero Infinite behavior prevents finite limit Hence continuity fails at x=0
As x approaches 0 from the right, \(\frac{1}{x}\rightarrow +\infty\) The limit is not a finite real number, so the right-hand limit does not exist in the real-number sense. Hence option C is correct. Option A is false because continuity requires a finite defined value. Options B and D are unrelated graphical interpretations.
- Option A β The function is undefined at x=0, so continuity is impossible there.
- Option B β Infinite discontinuity is not the same as a sharp corner.
- Option D β The graph never intersects the y-axis because x=0 is excluded from the domain.
Used: Elimination
Application:
- Remove options inconsistent with infinite behavior near x=0.
Final Logic:
- Infinite growth means no finite real right-hand limit exists.
"1/x near 0 β Infinity"
3 Let
\(f(x)=\left\{\begin{pmatrix}x+4, & x<3\\ 2x, & x\geq 3\end{pmatrix}\right.\)
Find the left-hand limit at x=3.
LHL uses expression for x<3 Substitute x=3 into x+4 Result equals 7
For the left-hand limit at x=3, we use the branch valid for x<3: \(f(x)=x+4\) Thus, \({limβ‘}_{x\rightarrow 3^{-}}f(x)=3+4=7\) Hence option D is correct. The right-side expression 2x is not used for the left-hand limit.
- Option A β 9 is not obtained from either branch at x=3.
- Option B β 6 comes from the right-side branch 2x, not the left-hand limit.
- Option C β 3 ignores the additional constant term in x+4.
Used: Substitution
Application:
- Substitute x=3 into the expression corresponding to x<3.
Final Logic:
- Left-hand limit uses the left-side formula only.
"LHL β Left branch"
4 Let a velocity component be defined as:
\(v(t)=\left\{\begin{pmatrix}t^{2}, & t<2\\ kt, & t\geq 2\end{pmatrix}\right.\)
For continuity at t=2, the right-hand limit must equal:
Continuity requires equal one-sided limits Left-hand limit equals \(2^{2}\) RHS must also equal 4
For continuity at t=2, \({limβ‘}_{t\rightarrow 2^{-}}v(t)={limβ‘}_{t\rightarrow 2^{+}}v(t)\) The left-hand limit is: \(2^{2}=4\) Therefore the right-hand limit must also equal 4. Hence option A is correct. The value of k would later be adjusted to satisfy this condition.
- Option B β Continuity requires equality with the left-hand limit, which is 4.
- Option C β Zero does not match the left-side behavior.
- Option D β The polynomial expression remains finite near t=2.
Used: Substitution
Application:
- Evaluate the left-hand limit and equate it with the right-hand limit.
Final Logic:
- Continuity demands both one-sided limits equal 4.
"Continuous join β Same value"
5 To compute the area under a curve \(y=f(x)\)on [a,b], which condition ensures integrability via continuity?
Continuous functions are integrable Unbroken graphs support area calculation NCERT links continuity with integration
A function continuous on a closed interval [a,b] is guaranteed to be integrable there. This allows meaningful computation of the area under the curve. Hence option B is correct. Discontinuities or breaks may complicate integration. Derivative behavior is unrelated to basic integrability requirements.
- Option A β Discontinuities may prevent direct integrability in standard situations.
- Option C β Differentiability is not the primary condition for definite integrability.
- Option D β Graph breaks indicate discontinuity, opposing smooth area computation.
Used: Contextual/Tonal Matching
Application:
- Connect continuity with the standard NCERT condition for integrability.
Final Logic:
- Continuous functions on closed intervals are integrable.
"Continuous curve β Integrable area"
6 Let
\(f(x)=\left\{\begin{pmatrix}x^{2}, & x\neq 1\\ 3, & x=1\end{pmatrix}\right.\)
Here,
\({limβ‘}_{x\rightarrow 1}f(x)=1\neq f(1)\)
This implies:
Limit exists but differs from value Continuity condition fails Removable discontinuity occurs at x=1
Since \({limβ‘}_{x\rightarrow 1}f(x)=1\) but \(f(1)=3\) the continuity condition fails. The discontinuity is removable because redefining f(1)=1 would restore continuity. Hence option C is correct. Options A and D are unrelated, while option B contradicts the unequal limit and function value.
- Option A β Discontinuity does not force the integral to become zero.
- Option B β Continuity requires limit and function value to be equal.
- Option D β A removable discontinuity does not produce infinite area.
Used: Elimination
Application:
- Compare the limit with the actual function value.
Final Logic:
- Unequal limit and value imply removable discontinuity.
"Limit exists, value differs β Removable"
7 Assertion (A):
The function
\(f(x)=\left\{\begin{pmatrix}-1, & x<0\\ 1, & x\geq 0\end{pmatrix}\right.\)
is continuous at x=0.
Reason (R):
The LHL at x=0 is β1 and the RHL is 1; since LHL β RHL, the limit does not exist.
One-sided limits are unequal Overall limit does not exist Therefore continuity fails at 0
The left-hand limit at x=0 is β1 while the right-hand limit is 1. Since these are unequal, the overall limit does not exist. Therefore the function cannot be continuous at x=0. Hence Assertion is false, but the Reason is true, making option D correct.
- Option A β The Reason is mathematically correct.
- Option B β The Assertion is false because unequal one-sided limits prevent continuity.
- Option C β The Assertion itself is incorrect, so both cannot be true together.
Used: Substitution
Application:
- Compute LHL and RHL directly from the piecewise definition.
Final Logic:
- Unequal one-sided limits destroy continuity.
"LHL β RHL β No continuity"
8 Arrange steps to check continuity of f(x) at x=a:
1. Compute \({limβ‘}_{x\rightarrow a}f(x)\)
2. Check if \({limβ‘}_{x\rightarrow a}f(x)=f(a)\)
3. Evaluate f(a)
4. Conclude continuity
First find the limit Then evaluate function value Compare and conclude continuity
To test continuity: First compute the limit at x=a. Then evaluate f(a). Next verify whether: \({limβ‘}_{x\rightarrow a}f(x)=f(a)\) Finally conclude continuity. Therefore the correct order is 1, 3, 2, 4. This follows the standard continuity checking procedure used in NCERT.
- Option B β Conclusion cannot come before calculations.
- Option C β Continuity cannot be concluded before comparing limit and function value.
- Option D β Equality cannot be checked before finding the required quantities.
Used: Contextual/Tonal Matching
Application:
- Follow the logical sequence used in continuity verification.
Final Logic:
- Compute, compare, then conclude.
"Limit β Value β Compare β Decide"
9 Match each function with the reason for discontinuity at x=0:
| List I | List II |
|---|---|
| 1. \(f(x)=1/x\) | a. LHL β RHL (jump discontinuity) |
| 2. \(f(x)=\left\{\begin{pmatrix}1, & x<0\\ 2, & x>0\end{pmatrix}\right.\) | b. Limit exists but β f(0) (removable) |
| 3. \(f(x)=\left\{\begin{pmatrix}x, & x\neq 0\\ 5, & x=0\end{pmatrix}\right.\) | c. Limit undefined (infinite discontinuity) |
| 4. \(f(x)=βxβ\) | d. Step/jump behavior (e.g., β1 to 0) |
\(1/x\) has infinite discontinuity Unequal one-sided limits create jumps Mismatched value gives removable discontinuity
\(1/x\) has infinite discontinuity at 0 β c. The piecewise constant function has unequal LHL and RHL β a. The third function has existing limit 0 but \(f(0)=5\)β removable discontinuity β b. The greatest integer function shows step behavior β d. Hence option B is correct.
- Option A β Incorrectly identifies removable and infinite discontinuities.
- Option C β Wrongly classifies the discontinuity types of multiple functions.
- Option D β The greatest integer function exhibits step behavior, not ordinary jump matching here.
Used: Option Grouping
Application:
- Associate each standard discontinuity type with its defining feature.
Final Logic:
- Correct classification uniquely determines the matching.
"β β Infinite, unequal β Jump, mismatch β Removable"
10 Which of the following functions have exactly one point of discontinuity?
i. \(f(x)=1/x\)
ii. \(f(x)=\left\{\begin{pmatrix}1, & x\neq 2\\ 5, & x=2\end{pmatrix}\right.\)
iii. \(f(x)=β£xβ£\)
\(1/x\) discontinuous only at 0 Second function discontinuous only at 2 |x| is continuous everywhere
\(1/x\) has exactly one discontinuity at x=0. The second function is discontinuous only at x=2 because the limit equals 1 while \(f(2)=5\). The modulus function |x| is continuous for all real numbers. Hence functions i and ii each have exactly one discontinuity. Therefore option A is correct, not D.
- Option B β |x| is continuous everywhere and has no discontinuity.
- Option C β Includes |x| incorrectly while omitting the second discontinuous function.
- Option D β Ignores the discontinuity of \(1/x\) at x=0.
Used: Elimination
Application:
- Check discontinuity points individually for each function.
Final Logic:
- Both i and ii each contain exactly one discontinuity point.
"1/x breaks at 0 only"
11 Identify the INCORRECT statement:
Continuous graphs are unbroken Pen lifting indicates breaks Continuity means smooth connection
A continuous graph can generally be drawn without lifting the pen, so option D is incorrect. Options A and B correctly describe graphical continuity and discontinuity. Option C is also correct because breaks in discontinuous graphs force interruption while drawing. NCERT informally explains continuity through uninterrupted graph tracing.
- Option A β Correct because continuity implies no breaks or gaps in the graph.
- Option B β Correct since a graphical break represents discontinuity.
- Option C β Correct because discontinuous graphs cannot usually be drawn in one stroke.
Used: Extreme Word Filter
Application:
- The word "always" signals an absolute statement likely to be incorrect.
Final Logic:
- Continuous graphs do not require lifting the pen.
"Continuous = One-stroke graph"
12 A function has a jump discontinuity at x=a.
If LHL = 5 and RHL = 12, what is the magnitude of the jump?
Jump size equals difference of limits Subtract LHL from RHL \(12-5=7\)
The magnitude of a jump discontinuity is: \(β£RHL-LHLβ£\) Given: \(RHL=12,LHL=5\) So, \(β£12-5β£=7\) Hence option A is correct. The jump represents the vertical gap between left-side and right-side limiting values.
- Option B β Uses only one-sided limit instead of their difference.
- Option C β Incorrectly takes the right-hand limit itself as jump magnitude.
- Option D β Adds the limits instead of subtracting them.
Used: Substitution
Application:
- Directly apply the jump discontinuity formula.
Final Logic:
- Jump magnitude equals absolute difference of one-sided limits.
"Jump = Right β Left"
13 If f(x) and g(x) are continuous functions, which is guaranteed to be continuous wherever defined?
Quotient continuity needs nonzero denominator Continuous functions preserve operations Undefined points must be excluded
The quotient of two continuous functions is continuous wherever the denominator is nonzero. Therefore: \(\frac{f(x)}{g(x)}\) is continuous only when \(g(x)\neq 0\). Hence option C is correct. Option A ignores denominator restrictions. Option B is not always defined for negative inputs. Option D is too restrictive.
- Option A β Division by zero causes discontinuity or undefined behavior.
- Option B β Square roots require nonnegative inputs for real-valued continuity.
- Option D β Many nonconstant functions are continuous, including polynomials and trigonometric functions.
Used: Elimination
Application:
- Remove options missing important domain conditions.
Final Logic:
- Quotients remain continuous only where denominator is nonzero.
"Quotient continuous if denominator β 0"
14 Why is the function \(f(x)=β£x^{2}-1β£\)continuous?
Polynomial functions are continuous Modulus function is continuous Composition preserves continuity
The function \(x^{2}-1\) is a polynomial and therefore continuous everywhere. The modulus function is also continuous. The composition: \(β£x^{2}-1β£\) remains continuous for all real x. Hence option D is correct. The function is defined everywhere and modulus works for both positive and negative inputs.
- Option A β The function is defined for every real number.
- Option B β Subtraction of continuous functions preserves continuity.
- Option C β Modulus is continuous for all real inputs, not just positive values.
Used: Option Grouping
Application:
- Use continuity properties of polynomial and modulus functions together.
Final Logic:
- Composition of continuous functions remains continuous.
"Continuous inside + continuous outside"
15 Let \(f(x)=k\) be constant. If \(f(3)=10\), find k.
Constant functions have same value everywhere Given function value fixes constant Thus k equals 10
For a constant function, \(f(x)=k\) for all x. Since: \(f(3)=10\) the constant value must be: \(k=10\) Hence option A is correct. The value does not depend on the input variable.
- Option B β Contradicts the given value \(f(3)=10\).
- Option C β Does not satisfy the constant function condition.
- Option D β Also inconsistent with the provided function value.
Used: Substitution
Application:
- Replace x=3 into the constant function definition.
Final Logic:
- Constant function value remains the same for every x.
"Constant means same everywhere"
16 For \(f(x)=x\), evaluate:
\({limβ‘}_{x\rightarrow a}f(x)\)
Identity function returns input itself As x approaches a, output approaches a Hence limit equals a
For the identity function: \(f(x)=x\) the output equals the input. Therefore as x approaches a, \({limβ‘}_{x\rightarrow a}x=a\) Hence option B is correct. The identity function is continuous everywhere and preserves approaching values directly.
- Option A β The limit equals a generally, not always zero.
- Option C β The limit is not fixed at 1 unless \(a=1\).
- Option D β The limit clearly exists for all real a.
Used: Substitution
Application:
- Observe direct input-output equality in the identity function.
Final Logic:
- Approaching x=a gives output approaching a.
"Identity keeps input unchanged"
17 Which function is continuous for all real x?
Polynomials are continuous everywhere Other functions have domain restrictions \(x^{2}\)defined for all real x
Polynomial functions are continuous for all real numbers. Hence \(x^{2}\)is continuous everywhere on R. The function \(1/x\) is undefined at 0, \(\sqrt{x}\)is defined only for \(x\geq 0\), and \(\ln\,x\) is defined only for positive x.
- Option A β Undefined at x=0, causing discontinuity.
- Option B β Not defined for negative real numbers.
- Option D β Logarithmic functions exist only for positive inputs.
Used: Elimination
Application:
- Check domain restrictions of each function.
Final Logic:
- Only the polynomial is continuous over all real numbers.
"Polynomials are always continuous"
18 If a function is defined only at x=5, it is:
Singleton domains have no nearby points Continuity conditions become automatic Vacuous continuity applies
If the domain contains only one point, there are no neighboring domain points approaching it. Hence continuity conditions are satisfied trivially. Therefore the function is considered continuous at that point. Thus option D is correct according to the formal definition of continuity on restricted domains.
- Option A β No discontinuity arises because there are no nearby domain points.
- Option B β The function is explicitly defined at x=5.
- Option C β Continuity has no relation to being "non-real."
Used: Contextual/Tonal Matching
Application:
- Apply the definition of continuity to a singleton domain.
Final Logic:
- No nearby points means continuity holds automatically.
"One-point domain β Continuous"
19 For continuity on [a,b], which is NOT required?
Closed interval continuity concerns interval only Outside behavior is irrelevant Endpoints and interior matter
To be continuous on [a,b], a function must be continuous at all interior points and satisfy endpoint continuity conditions at a and b. Behavior outside the interval does not matter. Therefore option A is correct because continuity beyond the interval is unnecessary.
- Option B β Left endpoint continuity is required on closed intervals.
- Option C β Right endpoint continuity is also required.
- Option D β Interior continuity is essential throughout the interval.
Used: Odd One Out
Application:
- Identify the option unrelated to continuity within the specified interval.
Final Logic:
- Outside continuity is irrelevant for interval continuity.
"Inside interval matters only"
20 For a function on [-2,2], continuity at x=2 requires checking:
Right endpoint has values only to left Endpoint continuity uses one-sided limit Left-hand approach is required
At the right endpoint x=2 of the interval [-2,2], values exist only from the left side within the domain. Therefore continuity is checked using: \({limβ‘}_{x\rightarrow 2^{-}}f(x)=f(2)\) Hence option B is correct. Right-hand limits are outside the interval domain.
- Option A β No domain points exist to the right of 2.
- Option C β Continuity at x=0 is unrelated to endpoint continuity at x=2.
- Option D β Continuity at β2 is a separate condition.
Used: Elimination
Application:
- Remove options involving unavailable domain directions.
Final Logic:
- Right endpoint continuity requires the left-hand limit only.
"Right endpoint β Left limit"
