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JEE Main 202228 JulyMorning Shift
Exam
JEE Main
Year
2022
Date
28 July
Shift
Morning Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2022 · 28 July · Morning Shift · Mathematics · Differential Equations

If y = y(x) , x ∈ (0, (π)/(2)) be the solution curve of the...

If y=y(x)y = y\left(x\right), x \in \left(0, \dfrac{\pi}{2}\right)be the solution curve of the differential equation</p><p>\left(\sin^{2}2x\right)\dfrac{dy}{dx} + \left(8sin⁡22x\sin^{2}2x + 2\sin 4x\right)y=y =

2e−4x(2sin⁡2x+cos⁡2x)2{e}^{- 4x}\left(2\sin 2x + \cos 2x\right),withwithy\left(\dfrac{\pi}{4}\right)=e−π= {e}^{- \pi}, then y(π6)y\left(\dfrac{\pi}{6}\right) is equal to

Options

  1. A23e−2π3\dfrac{2}{\sqrt{3}}{e}^{- \dfrac{2\pi}{3}}
  2. B23e2π3\dfrac{2}{\sqrt{3}}e\dfrac{2\pi}{3}
  3. C13e−2π3\dfrac{1}{\sqrt{3}}{e}^{- \dfrac{2\pi}{3}}
  4. D13e2π3\dfrac{1}{\sqrt{3}}e\dfrac{2\pi}{3}

Correct answer

A. 23e−2π3\dfrac{2}{\sqrt{3}}{e}^{- \dfrac{2\pi}{3}}

Step-by-step solution

Given, (sin⁡22x)dydx+(8sin⁡22x+2sin⁡4x)y=\left(\sin^{2}2x\right)\dfrac{dy}{dx} + \left(8\sin^{2}2x + 2\sin 4x\right)y =

2e−4x(2sin⁡2x+cos⁡2x)2{e}^{- 4x}\left(2\sin 2x + \cos 2x\right)

Now rewriting the given differential equation we get,

⇒dydx+(8+4cot⁡2x)y=2e−4xsin⁡22x(2sin⁡x+cos⁡2x)⇒ \dfrac{dy}{dx} + \left(8 + 4\cot 2x\right)y = \dfrac{2{e}^{- 4x}}{\sin^{2}2x}\left(2\sin x + \cos 2x\right)

Which is a linear differential equation.

Now calculating IF=e∫(8+4cot⁡2x)dx=e8x+2ln⁡(sin⁡2x)IF = {e}^{∫ \left(8 + 4\cot 2x\right)dx} = {e}^{8x + 2\ln \left(\sin 2x\right)}

=e8x⋅sin⁡22x= {e}^{8x} \cdot \sin^{2}2x

Now solution of differential equation is given by,

y×IF=∫2e−4x(2sin⁡2x+cos⁡2x)sin⁡22x×IFdxy \times IF = ∫ \dfrac{2{e}^{- 4x}\left(2\sin 2x + \cos 2x\right)}{\sin^{2}2x} \times IFdx

⇒y(e8x⋅sin⁡22x)=∫2e4x(2sin⁡2x+cos⁡2x)dx⇒ y\left({e}^{8x} \cdot \sin^{2}2x\right) = ∫ 2{e}^{4x}\left(2\sin 2x + \cos 2x\right)dx

⇒y(e8x⋅sin⁡22x)=e4x⋅sin⁡2x+C⇒ y\left({e}^{8x} \cdot \sin^{2}2x\right) = {e}^{4x} \cdot \sin 2x + C

Now given y(π4)=e−π⇒C=0y\left(\dfrac{\pi}{4}\right) = {e}^{- \pi} ⇒ C = 0

So, the equation of curve is given by y=e−4xsin⁡2xy = \dfrac{{e}^{- 4x}}{\sin 2x}

So, the value of y(π6)=e−4π6sin⁡(2⋅π6)=23e−2π3y\left(\dfrac{\pi}{6}\right) = \dfrac{{e}^{- 4\dfrac{\pi}{6}}}{\sin \left(2 \cdot \dfrac{\pi}{6}\right)} = \dfrac{2}{\sqrt{3}}{e}^{- \dfrac{2\pi}{3}}

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