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JEE Main 20262 AprilEvening Shift
Exam
JEE Main
Year
2026
Date
2 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Indefinite Integration

JEE Main 2026 · 2 April · Evening Shift · Mathematics · Indefinite Integration

Let f(x) = ∫ ((16x + 24)/(x^2 + 2x - 15)) dx . If f(4) = 14 _e(3)...

Let f(x)=∫(16x+24x2+2x−15)dxf(x) = \int \left(\dfrac{16x + 24}{x^2 + 2x - 15}\right) dx. If f(4)=14log⁡e(3)f(4) = 14 \log_e(3) and f(7)=log⁡e(2α⋅3β)f(7) = \log_e(2^{\alpha} \cdot 3^{\beta}), α,β∈N\alpha, \beta \in \mathbb{N}, then α+β\alpha + \beta is equal to:

Options

  1. A3131
  2. B3737
  3. C3939
  4. D4141

Correct answer

C. 3939

Step-by-step solution

The given integral is f(x)=∫(16x+24x2+2x−15)dxf(x) = \int \left(\dfrac{16x + 24}{x^2 + 2x - 15}\right) dx.

Factorizing the denominator, we get x2+2x−15=(x+5)(x−3)x^2 + 2x - 15 = (x + 5)(x - 3).

Using partial fractions, we can write:

16x+24(x+5)(x−3)=Ax+5+Bx−3\dfrac{16x + 24}{(x + 5)(x - 3)} = \dfrac{A}{x + 5} + \dfrac{B}{x - 3}

16x+24=A(x−3)+B(x+5)16x + 24 = A(x - 3) + B(x + 5)

Substituting x=3x = 3, we get 72=8B⇒B=972 = 8B \Rightarrow B = 9.

Substituting x=−5x = -5, we get −56=−8A⇒A=7-56 = -8A \Rightarrow A = 7.

Therefore, the integral becomes:

f(x)=∫(7x+5+9x−3)dxf(x) = \int \left(\dfrac{7}{x + 5} + \dfrac{9}{x - 3}\right) dx

f(x)=7log⁡e∣x+5∣+9log⁡e∣x−3∣+Cf(x) = 7 \log_e|x + 5| + 9 \log_e|x - 3| + C

Given f(4)=14log⁡e(3)f(4) = 14 \log_e(3), we substitute x=4x = 4:

f(4)=7log⁡e(9)+9log⁡e(1)+C=14log⁡e(3)+Cf(4) = 7 \log_e(9) + 9 \log_e(1) + C = 14 \log_e(3) + C

Since f(4)=14log⁡e(3)f(4) = 14 \log_e(3), we get C=0C = 0.

Thus, f(x)=7log⁡e∣x+5∣+9log⁡e∣x−3∣f(x) = 7 \log_e|x + 5| + 9 \log_e|x - 3|.

Now, substituting x=7x = 7:

f(7)=7log⁡e(12)+9log⁡e(4)f(7) = 7 \log_e(12) + 9 \log_e(4)

f(7)=7log⁡e(22⋅3)+9log⁡e(22)f(7) = 7 \log_e(2^2 \cdot 3) + 9 \log_e(2^2)

f(7)=7(2log⁡e(2)+log⁡e(3))+18log⁡e(2)f(7) = 7(2 \log_e(2) + \log_e(3)) + 18 \log_e(2)

f(7)=14log⁡e(2)+7log⁡e(3)+18log⁡e(2)f(7) = 14 \log_e(2) + 7 \log_e(3) + 18 \log_e(2)

f(7)=32log⁡e(2)+7log⁡e(3)f(7) = 32 \log_e(2) + 7 \log_e(3)

f(7)=log⁡e(232⋅37)f(7) = \log_e(2^{32} \cdot 3^7)

Comparing this with f(7)=log⁡e(2α⋅3β)f(7) = \log_e(2^{\alpha} \cdot 3^{\beta}), we get α=32\alpha = 32 and β=7\beta = 7.

Therefore, α+β=32+7=39\alpha + \beta = 32 + 7 = 39.

Answer: 3939
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