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JEE Main 202529 JanuaryMorning Shift
Exam
JEE Main
Year
2025
Date
29 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Definite Integration

JEE Main 2025 · 29 January · Morning Shift · Mathematics · Definite Integration

The integral (80 ∫_0^ (π)/(4) (( θ+ θ)/(9+16 2 θ)) d θ) is equal to...

The integral (80 \int_0^{\frac{\pi}{4}}\left(\frac{\sin \theta+\cos \theta}{9+16 \sin 2 \theta}\right) d \theta) is equal to :

Options

  1. A(3 \log _e 4)
  2. B(4 \log _{\mathrm{e}} 3)
  3. C(6 \log _e 4)
  4. D(2 \log _e 3)

Correct answer

B. (4 \log _{\mathrm{e}} 3)

Step-by-step solution

I=∫0π4(sin⁡θ+cos⁡θ9−16sin⁡2θ)dθ Take sin⁡θ−cos⁡θ=t(cos⁡θ+sin⁡θ)dθ=dt(sin⁡θ−cos⁡θ)2=t2⇒sin⁡2θ=1−t2θ=0→t=−1θ=π4→t=0I=∫−10dt9+16(1−t2)=116∫−10dt251616−t2=14[110log⁡∣ 5+4t5−4t]−10=140[0+log⁡e9]I=log⁡e94080I=2log⁡e980I=4log⁡e3\begin{aligned} & I=\int_0^{\frac{\pi}{4}}\left(\frac{\sin \theta+\cos \theta}{9-16 \sin 2 \theta}\right) d \theta \\ & \text{ Take } \sin \theta-\cos \theta=t \\ & (\cos \theta+\sin \theta) d \theta=d t \\ & (\sin \theta-\cos \theta)^2=t^2 \\ & \Rightarrow \sin 2 \theta=1-t^2 \\ & \theta=0 \rightarrow t=-1 \\ & \quad \theta=\frac{\pi}{4} \rightarrow t=0 \\ & I=\int_{-1}^0 \frac{d t}{9+16\left(1-t^2\right)} \\ & =\frac{1}{16} \int_{-1}^0 \frac{d t}{25} \frac{16}{16}-t^2 \\ & =\frac{1}{4}\left[\frac{1}{10} \log _{\left\lvert\, \frac{5+4 t}{}\right.}^{5-4 t}\right]_{-1}^0 \\ & =\frac{1}{40}\left[0+\log _e 9\right] \\ & I=\frac{\log _e 9}{40} \\ & 80 I=2 \log _e 9 \\ & 80 I=4 \log _e 3\end{aligned}
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