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JEE Main 202225 JulyMorning Shift
Exam
JEE Main
Year
2022
Date
25 July
Shift
Morning Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2022 · 25 July · Morning Shift · Mathematics · Differential Equations

The slope of the tangent to a curve C: y = y (x) at any point [ x,...

The slope of the tangent to a curve C:y=yC: y = y\left(x\right)atanypointat any point[ x, y )onitison it is\dfrac{2{e}^{2x} - 6{e}^{- x} + 9}{2 + 9{e}^{- 2x}}.If. IfCpassesthroughthepointspasses through the points\left(0, \dfrac{1}{2} + \dfrac{\pi}{2\sqrt{2}}\right)andand\left(\alpha, \dfrac{1}{2}{e}^{2\alpha}\right)thenthen{e}^{\alpha} is equal to

Options

  1. A3+23−2\dfrac{3 + \sqrt{2}}{3 - \sqrt{2}}
  2. B32(3+23−2)\dfrac{3}{\sqrt{2}}\left(\dfrac{3 + \sqrt{2}}{3 - \sqrt{2}}\right)
  3. C12(2+12−1)\dfrac{1}{\sqrt{2}}\left(\dfrac{\sqrt{2} + 1}{\sqrt{2} - 1}\right)
  4. D2+12−1\dfrac{\sqrt{2} + 1}{\sqrt{2} - 1}

Correct answer

B. 32(3+23−2)\dfrac{3}{\sqrt{2}}\left(\dfrac{3 + \sqrt{2}}{3 - \sqrt{2}}\right)

Step-by-step solution

Given,

dydx=2e2x−6e−x+92+9e−2x\dfrac{dy}{dx} = \dfrac{2{e}^{2x} - 6{e}^{- x} + 9}{2 + 9{e}^{- 2x}}

On rearranging we get,

dydx=e2x−6ex2e2x+9\dfrac{dy}{dx} = {e}^{2x} - \dfrac{6{e}^{x}}{2{e}^{2x} + 9}

Integrating both side we get,

y=e2x2−2tan⁡−1(2ex3)+cy = \dfrac{{e}^{2x}}{2} - \sqrt{2}\tan^{- 1}\left(\dfrac{\sqrt{2}{e}^{x}}{3}\right) + c

If the curve passes through the point \left(0, \dfrac{1}{2} + \dfrac{\pi}{2\sqrt{2}}\right)</p><p>Then</p><p>Thenc = \sqrt{2}\left(\dfrac{\pi}{4} + \tan^{- 1}\dfrac{\sqrt{2}}{3}\right)</p><p>So,curvewillbe</p><p>So, curve will bey = \dfrac{{e}^{2x}}{2} - \sqrt{2}\left(\tan^{- 1}\left(\dfrac{\sqrt{2}{e}^{x}}{3}\right) - \dfrac{\pi}{4} - \tan^{- 1}\dfrac{\sqrt{2}}{3}\right)</p><p>Againcurvepassesthroughthepoint</p><p>(α,12e2α)</p><p>Again curve passes through the point</p><p>\left(\alpha, \dfrac{1}{2}{e}^{2\alpha}\right)

Putting the value in curve equation we get,

e2α2=e2α2−2(tan⁡−1(2eα3)−π4−tan⁡−123)\dfrac{{e}^{2\alpha}}{2} = \dfrac{{e}^{2\alpha}}{2} - \sqrt{2}\left(\tan^{- 1}\left(\dfrac{\sqrt{2}{e}^{\alpha}}{3}\right) - \dfrac{\pi}{4} - \tan^{- 1}\dfrac{\sqrt{2}}{3}\right)

⇒tan⁡−1(2eα3)=π4+tan⁡−123⇒ \tan^{- 1}\left(\dfrac{\sqrt{2}{e}^{\alpha}}{3}\right) = \dfrac{\pi}{4} + \tan^{- 1}\dfrac{\sqrt{2}}{3}

⇒2eα3=tan⁡(π4+tan⁡−123)⇒ \dfrac{\sqrt{2}{e}^{\alpha}}{3} = \tan \left(\dfrac{\pi}{4} + \tan^{- 1}\dfrac{\sqrt{2}}{3}\right)

⇒2eα3=(tanπ4+tantan−1231−tanπ4×tantan−123)⇒ \dfrac{\sqrt{2}{e}^{\alpha}}{3} = \left(\dfrac{tan\dfrac{\pi}{4} + {tantan}^{- 1}\dfrac{\sqrt{2}}{3}}{1 - tan\dfrac{\pi}{4} \times {tantan}^{- 1}\dfrac{\sqrt{2}}{3}}\right)

⇒2eα3=⇒ \dfrac{\sqrt{2}{e}^{\alpha}}{3} =\left(\dfrac{1 + \dfrac{\sqrt{2}}{3}}{1 - \dfrac{\sqrt{2}}{3}}\right)</p><p></p><p>⇒ {e}^{\alpha} = \dfrac{3}{\sqrt{2}}\left(\dfrac{3 + \sqrt{2}}{3 - \sqrt{2}}\right)

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