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JEE Main 20245 AprilEvening Shift
Exam
JEE Main
Year
2024
Date
5 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Differentiation

JEE Main 2024 · 5 April · Evening Shift · Mathematics · Differentiation

If y(θ)=(2 θ+ 2 θ)/( 3 θ+4 2 θ+5 θ+2) , then at θ=(π)/(2), y^ +y^...

If y(θ)=2cos⁡θ+cos⁡2θcos⁡3θ+4cos⁡2θ+5cos⁡θ+2y(\theta)=\frac{2 \cos \theta+\cos 2 \theta}{\cos 3 \theta+4 \cos 2 \theta+5 \cos \theta+2}, then at θ=π2,y′′+y′+y\theta=\frac{\pi}{2}, y^{\prime \prime}+y^{\prime}+y is equal to :

Options

  1. A12\frac{1}{2}
  2. B1
  3. C2
  4. D32\frac{3}{2}

Correct answer

C. 2

Step-by-step solution

y=2cos⁡θ+2cos⁡2θ−14cos⁡3θ−3cos⁡θ+8cos⁡2θ−4+5cos⁡θ+2y=(2cos⁡2θ+2cos⁡θ−1)(2cos⁡2θ+2cos⁡θ−1)(2cos⁡θ+2)y=12(11+cos⁡θ)⇒θ=π2y=12y′=12(−1(1+cos⁡θ)2×(−sin⁡θ))⇒θ=π2y=12\begin{aligned} & y=\frac{2 \cos \theta+2 \cos ^2 \theta-1}{4 \cos ^3 \theta-3 \cos \theta+8 \cos ^2 \theta-4+5 \cos \theta+2} \\ & y=\frac{\left(2 \cos ^2 \theta+2 \cos \theta-1\right)}{\left(2 \cos ^2 \theta+2 \cos \theta-1\right)(2 \cos \theta+2)} \\ & y=\frac{1}{2}\left(\frac{1}{1+\cos \theta}\right) \\ & \Rightarrow \theta=\frac{\pi}{2} \quad y=\frac{1}{2} \\ & y^{\prime}=\frac{1}{2}\left(\frac{-1}{(1+\cos \theta)^2} \times(-\sin \theta)\right) \\ & \Rightarrow \theta=\frac{\pi}{2} \quad y=\frac{1}{2}\end{aligned}y′′=12[cos⁡θ(1+cos⁡θ)2−sin⁡θ(2)(1+cos⁡θ)(−sin⁡θ)(1+cos⁡θ)4]⇒θ=π2y=1\begin{aligned} y^{\prime \prime} & =\frac{1}{2}\left[\frac{\cos \theta(1+\cos \theta)^2-\sin \theta(2)(1+\cos \theta)(-\sin \theta)}{(1+\cos \theta)^4}\right] \\ & \Rightarrow \theta=\frac{\pi}{2} \quad y=1\end{aligned}$
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