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JEE Main 202331 JanuaryMorning Shift
Exam
JEE Main
Year
2023
Date
31 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Differentiation

JEE Main 2023 · 31 January · Morning Shift · Mathematics · Differentiation

Let y = f(x) = ^ 3 ((π)/(3)( ( π 3 2 (- 4 x ^ 3 + 5 x ^ 2 +...

Let y=f(x)=sin⁡3(π3(cos⁡(π32(−4x3+5x2+1)32)))y = f\left(x\right) = \sin^{3}\left(\dfrac{\pi}{3}\left(\cos \left(\dfrac{\pi}{3\sqrt{2}}\left(- 4{x}^{3} + 5{x}^{2} + 1\right)\dfrac{3}{2}\right)\right)\right). Then, at x=1x = 1,

Options

  1. A2y′+3π2y=02{y}^{'} + \sqrt{3}{\pi}^{2}y = 0
  2. B2y′+3π2y=02{y}^{'} + 3{\pi}^{2}y = 0
  3. C2y′−3π2y=0\sqrt{2}{y}^{'} - 3{\pi}^{2}y = 0
  4. Dy′+3π2y=0{y}^{'} + 3{\pi}^{2}y = 0

Correct answer

B. 2y′+3π2y=02{y}^{'} + 3{\pi}^{2}y = 0

Step-by-step solution

The given equation can be written as

y=sin⁡3y = \sin^{3}\left(\dfrac{\pi}{3}cosg\left(x\right)\right)

where,

g(x)=π32(−4x3+5x2+1)3/2g\left(x\right) = \dfrac{\pi}{3\sqrt{2}}{\left(- 4{x}^{3} + 5{x}^{2} + 1\right)}^{3 / 2}

⇒g′(x)=π22(−4x3+5x2+1)1/2(−12x2+10x)⇒ {g}^{'}\left(x\right) = \dfrac{\pi}{2\sqrt{2}}{\left(- 4{x}^{3} + 5{x}^{2} + 1\right)}^{1 / 2}\left(- 12{x}^{2} + 10x\right)

⇒g′(1)=π222(−2)=−π⇒ {g}^{'}\left(1\right) = \dfrac{\pi\sqrt{2}}{2\sqrt{2}}\left(- 2\right) = - \pi

And,

g(1)=2π3=(π−π3)g\left(1\right) = \dfrac{2\pi}{3} = \left(\pi - \dfrac{\pi}{3}\right)

Now,

y′=3sin⁡2(π3cosg(x))×cos⁡(π3cosg(x))×π3(−sing(x))g′(x){y}^{'} = 3\sin^{2}\left(\dfrac{\pi}{3}cosg\left(x\right)\right) \times \cos \left(\dfrac{\pi}{3}cosg\left(x\right)\right) \times \dfrac{\pi}{3}\left(- sing\left(x\right)\right){g}^{'}\left(x\right)

y′(1)=3sin⁡2(−π6)⋅cos⁡(π6)⋅π3(−sin2π3)g′(1){y}^{'}\left(1\right) = 3\sin^{2}\left(- \dfrac{\pi}{6}\right) \cdot \cos \left(\dfrac{\pi}{6}\right) \cdot \dfrac{\pi}{3}\left(- sin\dfrac{2\pi}{3}\right){g}^{'}\left(1\right)

y′(1)=34⋅32⋅π3(−32)(−π)=3π216{y}^{'}\left(1\right) = \dfrac{3}{4} \cdot \dfrac{\sqrt{3}}{2} \cdot \dfrac{\pi}{3}\left(\dfrac{- \sqrt{3}}{2}\right)\left(- \pi\right) = \dfrac{3{\pi}^{2}}{16}

y(1)=sin⁡3(π3cos2π3)=−18y\left(1\right) = \sin^{3}\left(\dfrac{\pi}{3}cos\dfrac{2\pi}{3}\right) = - \dfrac{1}{8}

Therefore,

2y′(1)+3π2y(1)=02{y}^{'}\left(1\right) + 3{\pi}^{2}y\left(1\right) = 0

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