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JEE Main 202325 JanuaryMorning Shift
Exam
JEE Main
Year
2023
Date
25 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2023 · 25 January · Morning Shift · Mathematics · Differential Equations

Let y = y (x) be the solution curve of the differential equation...

Let y=yy = y\left(x\right)bethesolutioncurveofthedifferentialequationbe the solution curve of the differential equation\dfrac{dy}{dx} = \dfrac{y}{x}\left(1 + {x}^{2}\left(1 + \log_{e}x\right)\right),,x > 0, y ( 1 ) = 3.Then. Then\dfrac{{y}^{2} ( x )}{9} is equal to :

Options

  1. A\dfrac{{x}^{2}}{5 - 2{x}^{3}\left(2 + \log_{e}{x}^{3}\right)}
  2. Bx22x3(2+log⁡ex3)−3\dfrac{{x}^{2}}{2{x}^{3}\left(2 + \log_{e}{x}^{3}\right) - 3}
  3. Cx23x3(1+log⁡ex2)−2\dfrac{{x}^{2}}{3{x}^{3}\left(1 + \log_{e}{x}^{2}\right) - 2}
  4. D\dfrac{{x}^{2}}{7 - 3{x}^{3}\left(2 + \log_{e}{x}^{2}\right)}

Correct answer

A. \dfrac{{x}^{2}}{5 - 2{x}^{3}\left(2 + \log_{e}{x}^{3}\right)}

Step-by-step solution

Given differential equation can be rewritten as,

dydx−yx=y3(1+log⁡ex)\dfrac{dy}{dx} - \dfrac{y}{x} = {y}^{3}\left(1 + \log_{e}x\right)

1y3dydx−1xy2=1+log⁡ex\dfrac{1}{{y}^{3}}\dfrac{dy}{dx} - \dfrac{1}{{xy}^{2}} = 1 + \log_{e}x

Let \left(- \dfrac{1}{{y}^{2}}\right) = t ⇒ \dfrac{2}{{y}^{3}}\dfrac{dy}{dx} = \dfrac{dt}{dx}</p><p></p><p>∴ \dfrac{dt}{2dx} + \dfrac{t}{x} = \left(1 + \log_{e}x\right)</p><p></p><p>⇒ \dfrac{dt}{dx} + \dfrac{2t}{x} = 2\left(1 + \log_{e}x\right) . . . . . . . . . . ( 1 )</p><p>Weknowthesolutionofthedifferentialequation</p><p>We know the solution of the differential equation\dfrac{dy}{dx} + Py = Qisgivenby,</p><p>is given by,</p><p>{ye}^{∫ Pdx} = ∫ {Qe}^{∫ Pdx} + C ( WhereI . F . = {e}^{∫ Pdx} )</p><p>Therefore,onsolvingequation(1)weget,</p><p>I.F.</p><p>Therefore, on solving equation(1) we get,</p><p>I.F.= {e}^{∫ \dfrac{2}{x}dx} = {x}^{2}</p><p></p><p>\dfrac{- {x}^{2}}{{y}^{2}} = \dfrac{2}{3}\left(\left(1 + \log_{e}x\right){x}^{3} - \dfrac{{x}^{3}}{3}\right) + C . . . . . . ( 2 )</p><p>Given,</p><p>Given,y ( 1 ) = 3</p><p></p><p>⇒ \dfrac{1}{9} = - 2\left(\dfrac{1}{3} - \dfrac{1}{9}\right) + C</p><p></p><p>∴ C = \dfrac{5}{9}</p><p>NowputtingvalueofCinequation(2)weget,</p><p></p><p>Now putting value of C in equation(2) we get,</p><p>\dfrac{{y}^{2}}{9} = \dfrac{{x}^{2}}{5 - 2{x}^{3}\left(2 + \log_{e}{x}^{3}\right)}$

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