JEE Main · Mathematics ↓ Falling

Limits, Continuity and Differentiability appeared 52 times across 3 years — 6% of Mathematics. This question is from Continuity and Differentiability of Piecewise Functions.

Year 2026 2025 2024 Total
Questions 12 24 16 52

Let f(x) = cases 3x, & x < 0 1 + x + [ x ], x + 2 [ x ] , & 0 ≤ x ≤ 2 5, & x > 2 cases where [.] denotes greatest integer function. If α and β are the number of points, where f is not continuous and is not differentiable, respectively, then α + β equals....

Numerical Answer Type:
Enter a numerical value Answer: 5 to 5 +4 marks

Solution & Explanation

Related Formula

A function is discontinuous if left-hand and right-hand limits mismatch at boundary transitions. Non-differentiability occurs at discontinuities or sharp turns.

Core Logic

Simplify the greatest integer component [x] by expanding over integer intervals:

Continuity and Differentiability of Piecewise Functions diagram for Q74 - JEE Main 2025 Morning
Continuity and Differentiability of Piecewise Functions diagram for Q74 - JEE Main 2025 Morning

f(x) = cases 3x, & x < 0 x, & 0 ≤ x < 1 x + 2, & 1 ≤ x < 2 5, & x > 2 cases
Step 1: Testing Continuity Limits

Check continuity at structural boundaries: At x = 0: LHM = 0, RHM = 0 Continuous. At x = 1: LHM = 1, RHM = 3 Discontinuous. At x = 2: LHM = 4, RHM = 5 Discontinuous.

Thus, α = 2 points of discontinuity (x in 1, 2).

Step 2: Testing Differentiability Parameters

Discontinuities automatically introduce non-differentiability. Now check smooth corners at the remaining continuous transition x = 0:

f^ (0^-) = 3, f^ (0^+) = 1 Not differentiable at x=0.

Thus, β = 3 points of non-differentiability (x in 0, 1, 2).

α + β = 2 + 3 = 5
Pattern Recognition

Discontinuities automatically break differentiability. Always count them first before checking derivatives at smooth corner points.

Chapter Mix

Class 12 Maths: Limits, Continuity and Differentiability

Reference Study Guides

More Limits, Continuity and Differentiability Previous-Year Questions — Page 8

Q73 jee_main_2025_29_jan_morning Sandwich Theorem and Greatest Integer Function
Let [t] be the greatest integer less than or equal to t. Then the least value of p in N for which x → 0⁺ ( x ( [ 1x ] + [ 2x ] + + [ px ] ) - x² ( [ 1x² ] + [ 2²x² ] + + [ 9²x² ] ) ) ≥ 1 is equal to
Numerical Answer. Answer: 24

Solution

Related Formula
x → 0^+ x [ (k)/(x) ] = k Σk=1ⁿ k = (n(n+1))/(2), Σk=1ⁿ k² = (n(n+1)(2n+1))/(6)
Core Logic

Using properties of Greatest Integer Function limits, as x → 0^+, fraction values diverge cleanly to continuous variable distributions:

x → 0^+ x [ (k)/(x) ] = k Σk=1p k = (p(p+1))/(2)

Similarly, for the second block component part:

x → 0^+ x² [ (k²)/(x²) ] = k² Σk=1⁹ k² = (9 × 10 × 19)/(6) = 285
Step 1: Setup Inequality Formulation

Combine evaluated limits component parts:

(p(p+1))/(2) - 285 ≥ 1 (p(p+1))/(2) ≥ 286 p(p+1) ≥ 572
Step 2: Solve for least natural number

Evaluate product bounds of adjacent integers: If p = 23 23 × 24 = 552 (False) If p = 24 24 × 25 = 600 (True) Therefore, the least natural value of p is 24.

Pattern Recognition

Greatest Integer fractions simplify directly to standard scalar values inside limits evaluated at infinity or zero, letting you drop brackets and treat them as arithmetic sequences.

Chapter Mix

Class 11 Mathematics: Limits

Q15 jee_main_2024_01_february_morning Continuity and Differentiability of Piecewise Functions
Let f:Rarrow R be defined as f(x)= cases(a-b 2x)/(x²) & , & x<0 x²+cx+2 & , & 0≤ x≤1 2x+1 & , & x>1 cases If f is continuous everywhere in R and m is the number of points where f is NOT differentiable, then m+a+b+c equals:
  • A. 1
  • B. 4
  • C. 3
  • D. 2

Solution

Related Formula

For a function to be continuous at a boundary point x = x₀, the left-hand limit, right-hand limit, and exact function value must all match:

x → x₀^- f(x) = x → x₀^+ f(x) = f(x₀)
Core Logic

Let's enforce continuity at the critical boundaries, x = 1 and x = 0:

  • Continuity at x = 1:
f(1^-) = f(1) = 1² + c(1) + 2 = 3 + c f(1^+) = 2(1) + 1 = 3

Equating both configurations: 3 + c = 3 c = 0.

  • Continuity at x = 0:
f(0^+) = f(0) = 0² + 0 + 2 = 2 f(0^-) = h → 0 (a - b (2h))/(h²)

Using the Taylor expansion (2h) = 1 - (4h²)/(2!) + (16h⁴)/(4!) - = 1 - 2h² + (2)/(3)h⁴ -

h → 0 (a - b(1 - 2h² + (2)/(3)h⁴ - ))/(h²) = h → 0 ((a-b) + 2bh² - (2)/(3)bh⁴ + )/(h²)

For the limit to exist and remain finite, the constant term must vanish: a - b = 0 a = b. The value of the limit is then equal to 2b. To satisfy continuity: 2b = 2 b = 1 a = 1.

Step 1: Checking Differentiability at x = 0

Evaluating the Left-Hand Derivative (LHD) at x = 0 using values a=1, b=1:

LHD = h → 0 (f(-h) - f(0))/(-h) = h → 0 ((1 - (2h))/(h²) - 2)/(-h) LHD = h → 0 ((2 - (2)/(3)h² + ) - 2)/(-h) = h → 0 (2)/(3)h = 0

Evaluating the Right-Hand Derivative (RHD) at x = 0:

RHD = h → 0 (f(h) - f(0))/(h) = h → 0 ((h² + 2) - 2)/(h) = h → 0 h = 0

Since LHD = RHD = 0, the function is fully differentiable at x = 0.

Step 2: Checking Differentiability at x = 1

Evaluating derivatives at x = 1 with parameter c = 0:

  • For 0 ≤ x ≤ 1, f(x) = x² + 2 f'(x) = 2x f'(1^-) = 2.
  • For x > 1, f(x) = 2x + 1 f'(x) = 2 f'(1^+) = 2.
  • Since the left derivative equals the right derivative at x = 1, the function is differentiable at x = 1.

    Thus, the function is differentiable everywhere, giving m = 0 points of non-differentiability.

Step 3: Finding the Requested Evaluation Sum

Now substitute the values m=0, a=1, b=1, c=0 into the target equation:

m + a + b + c = 0 + 1 + 1 + 0 = 2
Pattern Recognition

Sees: Continuity conditions paired with rational surd trigonometric expansion. Shortcut: When tracking indeterminate limits like (a-b 2x)/(x²), matching expansions row by row prevents typical computation errors encountered with standard L'Hopital differentiation loops.

Chapter Mix

Class 12 Mathematics: Limits, Continuity and Differentiability

Q25 jee_main_2024_01_february_morning One Sided Limits
Let {x} denote the fractional part of x and f(x)= ⁻¹(1-x²) ⁻¹(1-x)x-x³, x≠0. If L and R respectively denotes the left hand limit and the right hand limit of f(x) at x=0 then 32π²(L²+R²) is equal to
Numerical Answer. Answer: 18 to 18

Solution

Related Formula

Definition of fractional part function:

  • For x → 0^+, x = x - 0 = x.
  • For x → 0^-, x = x - (-1) = x + 1.
Core Logic

Let's evaluate the left-hand limit (L) and right-hand limit (R) separately by setting up substitution parameters around the point x=0.

Step 1: Evaluate Right Hand Limit (R)

As x → 0^+, substitute x = h where h → 0:

R = h → 0 ⁻¹(1-h²) ⁻¹(1-h)h(1-h²) = h → 0 ⁻¹(1-h²)h · ( ⁻¹11) = (π)/(2) h → 0 ⁻¹(1-h²)h

Let ⁻¹(1-h²) = θ 1-h² = θ h² = 1 - θ = 2 ²(θ/2). As h → 0, θ → 0, so h ≈ θ√(2):

R = (π)/(2) θ → 0 θ θ√(2) = π√(2)
Step 2: Evaluate Left Hand Limit (L)

As x → 0^-, let x = -h x = 1-h where h → 0:

L = h → 0 ⁻¹(1-(1-h)²) ⁻¹(1-(1-h))(1-h) - (1-h)³ L = h → 0 ⁻¹(2h-h²) ⁻¹h(1-h)[1 - (1-h)²] = h → 0 ⁻¹(0) ⁻¹h1 · (2h-h²) L = (π)/(2) h → 0 ( ⁻¹hh · (1)/(2-h) ) = (π)/(2) · 1 · (1)/(2) = (π)/(4)
Step 3: Calculate the Target Value

Substituting the computed limits L = (π)/(4) and R = π√(2) into the target expression:

32π²(L²+R²) = (32)/(π²) ( (π²)/(16) + (π²)/(2) ) = 32 ( (1)/(16) + (1)/(2) ) = 2 + 16 = 18
Pattern Recognition

Sees: Discontinuous fractional part function framing an indeterminate limit form. Trap: Be extremely careful when managing fractional limits below zero: x → 1 when x → 0^-, transforming expressions significantly compared to right-hand approaches.

Chapter Mix

Class 12 Mathematics: Limits, Continuity and Differentiability Class 11 Mathematics: Relations and Functions

Q jee_main_2024_29_january_evening Higher Order Derivatives
Let y = ₑ((1 - x²)/(1 + x²) ), -1 < x < 1. Then at x = (1)/(2), the value of 225(y' - y'') is equal to
  • A. 732
  • B. 746
  • C. 742
  • D. 736

Solution

Related Formula
y = ln(1 - x²) - ln(1 + x²)
Core Logic

Let us differentiate the simplified logarithm form:

y' = (-2x)/(1 - x²) - (2x)/(1 + x²) = -2x ( (1 + x² + 1 - x²)/(1 - x⁴) ) = (-4x)/(1 - x⁴)

Now, computing the second derivative y'' using the quotient rule:

y'' = (-4(1 - x⁴) - (-4x)(-4x³))/((1 - x⁴)²) = (-4 + 4x⁴ - 16x⁴)/((1 - x⁴)²) = (-4(1 + 3x⁴))/((1 - x⁴)²)
Step 1: Finding the Combined Value

Let us substitute x = (1)/(2) into the expressions:

1 - x⁴ = 1 - (1)/(16) = (15)/(16) y' = (-4(1/2))/(15/16) = (-2)/(15/16) = -(32)/(15) y'' = (-4(1 + 3/16))/((15/16)²) = (-4(19/16))/(225/256) = -(19)/(4) × (256)/(225) = -(19 × 64)/(225) = -(1216)/(225)
Step 2: Resolving the Target Multiplier

Compute y' - y'':

y' - y'' = -(32)/(15) - (-(1216)/(225)) = -(480)/(225) + (1216)/(225) = (736)/(225)

Multiplying this by 225:

225(y' - y'') = 225 × (736)/(225) = 736
Pattern Recognition

Always break log quotient blocks into independent terms before differentiating (ln(a)/(b) = ln a - ln b). Differentiating fractions directly invites errors.

Chapter Mix

Class 12 Mathematics: Continuity and Differentiability

Q30 jee_main_2024_29_january_evening Leibniz Rule and Limits
Let the slope of the line 45x + 5y + 3 = 0 be 27r₁ + (9r₂)/(2) for some r₁, r₂ in R. Then x arrow 3 (∫₃x (8t²)/((3r₂ x)/(2) - r₂ x² - r₁ x³ - 3x) dt) is equal to
Numerical Answer. Answer: 12 to 12

Solution

Related Formula

Using the Newton-Leibniz formula for differentiating an integral:

(d)/(dx) ( ∫ₐx f(t) dt ) = f(x)
Core Logic

The line equation is 45x + 5y + 3 = 0 y = -9x - (3)/(5). Its slope is -9. Equating the slope expressions:

27r₁ + (9r₂)/(2) = -9 3r₁ + (r₂)/(2) = -1 (i)
Step 1: Applying L'Hopital's Rule to the Limit

The limit is in the (0)/(0) form as x arrow 3. Differentiating the numerator and denominator using L'Hopital's Rule:

Limit = x arrow 3 (8x²)/((3r₂)/(2) - 2r₂ x - 3r₁ x² - 3)
Step 2: Evaluating the Target Denominator Value

Substitute x = 3 into the differentiated structure:

Denominator = (3r₂)/(2) - 6r₂ - 27r₁ - 3 = -(9r₂)/(2) - 27r₁ - 3 = -9(3r₁ + (r₂)/(2)) - 3

From equation (i), we substitute 3r₁ + (r₂)/(2) = -1:

Denominator = -9(-1) - 3 = 9 - 3 = 6

Evaluating the full limit:

Limit = (8(3)²)/(6) = (72)/(6) = 12
Pattern Recognition

L'Hopital transformations reduce parameter sets back into exact multiples of the initial constraint formula. This avoids solving for r₁ and r₂ individually.

Chapter Mix

Class 12 Mathematics: Limits, Continuity and Differentiability

More Limits, Continuity and Differentiability Questions — jee_main_2025_28_jan_morning

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