If t→ 0(∫₀¹ (3x + 5)^t dx)(1)/(t) = (α)/(5e)((8)/(5))(2)/(3), then α is equal to

Numerical Answer Type:
Enter a numerical value Answer: 64 to 64 +4 marks

Solution & Explanation

Related Formula

Standard indeterminacy layout resolution rules for limits matching form 1^∞:

t → 0 [g(t)](1)/(t) = e^ t → 0 (g(t) - 1)/(t)
Core Logic

Evaluate structural integration base at boundary limit initialization state t → 0:

∫₀¹ 1 dx = 1

This confirms it matches an indeterminate form of type 1^∞.

Step 1: Apply Taylor Series or L'Hopital's Theorem

Compute limits of logarithmic integration properties inside exponential power indices:

Exponent Expression = t → 0 ∫₀¹ (3x+5)^t dx - 1t

Applying L'Hopital's theorem to differentiate the numerator with respect to t yields:

∫₀¹ (3x+5)^t ln(3x+5) dx

Evaluating this at t = 0 gives:

∫₀¹ ln(3x+5) dx
Step 2: Complete the Final Form Match

Integrating via parts results in logarithmic value updates:

[ ((3x+5)ln(3x+5) - (3x+5))/(3) ]₀¹ = (8ln 8 - 5ln 5 - 3)/(3)

Passing components back through exponential foundations transforms terms to:

e(8ln 8 - 5ln 5 - 3)/(3) = ((8)/(5))(2)/(3) · ((64)/(5e))

Comparing with the target expression (α)/(5e)((8)/(5))(2)/(3) isolates the numerical solution directly: α = 64

Pattern Recognition

Treating 1^∞ structural transformations using logarithmic derivatives allows managing complex functions containing multiple integral boundaries effectively.

Chapter Mix

Class 11 Mathematics: Limits Class 12 Mathematics: Definite Integration

Reference Study Guides

More Limits Previous-Year Questions

Q10 jee_main_2026_21_jan_morning 1^infinity Limit Form with L'Hopital's Rule
Let f: R → (0, ∞) be a twice differentiable function such that f(3) = 18 , f'(3) = 0 and f''(3) = 4 . Then x → 1 ( ₑ ( (f(2 + x))/(f(3)) )(18)/((x-1)²) ) is equal to:
  • A. 1
  • B. 9
  • C. 2
  • D. 18

Solution

Related Formula

For a limit of 1∞ form, x → a [g(x)]h(x) equals:

e^ x → a h(x)[g(x) - 1]
Core Logic

Let T = x → 1 ( (f(x + 2))/(f(3)) )(18)/((x - 1)²). As x → 1, (f(x+2))/(f(3)) → (f(3))/(f(3)) = 1. The exponent goes to ∞. This is a standard 1∞ form.

T = e^ x → 1 (18)/((x - 1)²) ( (f(x + 2) - f(3))/(f(3)) )
Step 1: Simplify Exponent Limit

Given f(3) = 18:

T = e^ x → 1 (18)/((x - 1)²) ( (f(x + 2) - f(3))/(18) ) T = e^ x → 1 (f(x + 2) - f(3))/((x - 1)²)

This is a (0)/(0) form limit.

Step 2: Apply L'Hopital's Rule

Differentiate numerator and denominator w.r.t x:

T = e^ x → 1 (f'(x + 2))/(2(x - 1))

This is still a (0)/(0) form since f'(3) = 0. Apply L'Hopital's Rule again:

T = e^ x → 1 (f''(x + 2))/(2)

Substitute x = 1:

T = e(f''(3))/(2)
Step 3: Final Calculation

Given f''(3) = 4:

T = e(4)/(2) = e²

The question asks for ₑ(T):

ₑ(T) = ₑ(e²) = 2
Pattern Recognition

When expanding f(x) around an extrema (f'(a)=0) inside a 1∞ limit form, double L'Hopital isolates the second derivative divided by the Taylor factorial (2! = 2). The limit elegantly shrinks directly to f''(a)/2.

Chapter Mix

Class 11 Maths: Limits and Derivatives Class 12 Maths: Limits, Continuity and Differentiability

Q21 jee_main_2026_21_jan_evening Limits of Sum
Let [·] denote the greatest integer function and f(x)= n→∞ 1n³Σk=1ⁿ[ k²3x]. Then 12Σj=1∞f(j) is equal to
Numerical Answer. Answer: 2 to 2

Solution

Related Formula
Sandwich Theorem for greatest integer function: x - 1 < [x] ≤ x Σk=1ⁿ k² = (n(n+1)(2n+1))/(6)
Core Logic

Evaluate f(x) using Squeeze Theorem on the summation bounds due to the Greatest Integer Function.

(k²)/(3^x) - 1 < [(k²)/(3^x)] ≤ (k²)/(3^x)
Step 1: Evaluate Limit f(x)

Sum over bounds:

Σk=1ⁿ ( (k²)/(3^x) - 1 ) < Σk=1ⁿ [ (k²)/(3^x) ] ≤ Σk=1ⁿ (k²)/(3^x) (1)/(3^x) (n(n+1)(2n+1))/(6) - n < Σk=1ⁿ [ (k²)/(3^x) ] ≤ (1)/(3^x) (n(n+1)(2n+1))/(6)

Divide by n³ and apply limit n → ∞:

n → ∞ ( (2n³ + 3n² + n)/(6n³ · 3^x) - (1)/(n²) ) < f(x) ≤ n → ∞ (2n³ + 3n² + n)/(6n³ · 3^x) f(x) = (2)/(6 · 3^x) = (1)/(3 · 3^x) = 13x+1
Step 2: Evaluate Final Summation

We need 12Σj=1∞ f(j):

12 Σj=1∞ 13j+1 = 12 ( (1)/(3²) + (1)/(3³) + … )

This is an infinite geometric progression with a = (1)/(9) and r = (1)/(3).

Sum = (a)/(1 - r) = (1/9)/(1 - 1/3) = (1/9)/(2/3) = (1)/(6)

Finally, 12 × (1)/(6) = 2.

Pattern Recognition

When evaluating infinite limits over greatest integer sums n → ∞ 1np+1 Σ [k^p/C], the G.I.F brackets can be safely replaced by exact values due to Sandwich theorem bounding the -1 residual to 0.

Chapter Mix

Class 11 Maths: Limits, Continuity and Differentiability Class 11 Maths: Sequence and Series

Q5 jee_main_2026_22_january_evening Limits using Expansion
If x → 0 e(a-1)x + 2 bx + (c-2)e-xx x - ₑ(1+x) = 2, then a² + b² + c² is equal to:
  • A. 5
  • B. 3
  • C. 7
  • D. 9

Solution

Related Formula

Standard Taylor series expansions:

e^x = 1 + x + (x²)/(2!) + , x = 1 - (x²)/(2!) + , ₑ(1+x) = x - (x²)/(2) +
Core Logic

Expand numerator and denominator around x = 0: Denominator: x(1 - (x²)/(2)) - (x - (x²)/(2)) = (x²)/(2) + O(x³). For limit to be finite, coefficients of x⁰ and x¹ in numerator must be zero:

  • Coefficient of x⁰: 1 + 2 + c - 2 = 0 c = -1
  • Coefficient of x¹: (a-1) - (c-2) = 0 a - 1 + 3 = 0 a = -2
Step 1: Coefficient of x^2

Numerator coefficient of x² is ((a-1)²)/(2) - b² + (c-2)/(2). Given limit value is 2:

(((a-1)²)/(2) - b² + (c-2)/(2))/(1/2) = 2 (9)/(2) - b² - (3)/(2) = 1 b² = 2
Step 2: Final Calculation
a² + b² + c² = (-2)² + 2 + (-1)² = 4 + 2 + 1 = 7
Pattern Recognition

Match powers of x in Taylor series to resolve indeterminate limit form (0)/(0).

Chapter Mix

Class 11 Maths: Limits, Continuity and Differentiability

Q15 jee_main_2026_22_january_evening Points of Discontinuity and Min Function
Let [·] denote the greatest integer function, and let f(x) = √(2)x, x². Let S = x in (-2,2) : the function g(x) = |x|[x²] is discontinuous at x. Then Σx in S f(x) equals:
  • A. 2 - √(2)
  • B. 2√(6) - 3√(2)
  • C. 1 - √(2)
  • D. √(6) - 2√(2)

Solution

Related Formula

Greatest integer function [x²] is discontinuous where x² takes integer values, except possibly where |x| = 0.

Core Logic

In (-2, 2), x² in [0, 4). Integer values occur at x = 0, ± 1, ±√(2), ±√(3). At x = 0, g(0) = 0 and x → 0 g(x) = 0, so g(x) is continuous at x = 0. Points of discontinuity: S = -1, 1, -√(2), √(2), -√(3), √(3).

Step 1: Evaluate f(x) for x in S

For f(x) = √(2)x, x²:

  • f(-1) = -√(2), 1 = -√(2)
  • f(1) = √(2), 1 = 1
  • f(-√(2)) = -2, 2 = -2
  • f(√(2)) = 2, 2 = 2
  • f(-√(3)) = -√(6), 3 = -√(6)
  • f(√(3)) = √(6), 3 = √(6)
Step 2: Summation
Σx in S f(x) = -√(2) + 1 - 2 + 2 - √(6) + √(6) = 1 - √(2)
Pattern Recognition

Check origin continuity explicitly for |x|[x²]; evaluate √(2)x, x² case-by-case on set S.

Chapter Mix

Class 12 Maths: Limits, Continuity and Differentiability

Q9 jee_main_2026_23_january_morning Continuity
Let f(x) = cases (ax² + 2ax + 3)/(4x² + 4x - 3), & x ≠ -(3)/(2), (1)/(2) b, & x = -(3)/(2), (1)/(2) cases be continuous at x = -(3)/(2). If fof(x) = (7)/(5), then x is equal to:
  • A. 2
  • B. 1
  • C. 0
  • D. 1.4

Solution

Core Logic

For f(x) to be continuous at x = -(3)/(2), the limit as x → -(3)/(2) must exist and equal f(-(3)/(2)) = b.

x → -3/2 (ax² + 2ax + 3)/((2x - 1)(2x + 3))

Since the denominator is zero at x = -(3)/(2), for the limit to exist, the numerator must also be zero at x = -(3)/(2).

Step 1: Determine 'a'

Set the numerator to 0 at x = -(3)/(2):

a(-(3)/(2))² + 2a(-(3)/(2)) + 3 = 0 (9a)/(4) - 3a + 3 = 0 (-3a)/(4) + 3 = 0 ⇒ (3a)/(4) = 3 ⇒ a = 4
Step 2: Simplify f(x)

Substitute a = 4 into f(x) for x ≠ -(3)/(2), (1)/(2):

f(x) = (4x² + 8x + 3)/((2x - 1)(2x + 3))

Factorizing the numerator:

4x² + 8x + 3 = (2x + 1)(2x + 3)

Thus, f(x) = ((2x + 1)(2x + 3))/((2x - 1)(2x + 3)) = (2x + 1)/(2x - 1) for x ≠ -(3)/(2).

Step 3: Solve f(f(x)) = 7/5

Evaluate fof(x):

f(f(x)) = f((2x + 1)/(2x - 1)) = (2((2x + 1)/(2x - 1)) + 1)/(2((2x + 1)/(2x - 1)) - 1) = (2(2x + 1) + (2x - 1))/(2(2x + 1) - (2x - 1)) = (4x + 2 + 2x - 1)/(4x + 2 - 2x + 1) = (6x + 1)/(2x + 3)

Equate to (7)/(5):

(6x + 1)/(2x + 3) = (7)/(5) ⇒ 5(6x + 1) = 7(2x + 3) 30x + 5 = 14x + 21 ⇒ 16x = 16 ⇒ x = 1
Pattern Recognition

Indeterminate forms at points of continuity explicitly lock polynomial coefficients. Always resolve the 0/0 form to extract missing variables before addressing composite functions.

Chapter Mix

Class 12 Maths: Limits, Continuity and Differentiability

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