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JEE Main 20231 FebruaryEvening Shift
Exam
JEE Main
Year
2023
Date
1 February
Shift
Evening Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2023 · 1 February · Evening Shift · Mathematics · Differential Equations

Let = exp( x ^ β y ^ γ ) be the solution of the differential...

Let \alphax=exp(xβyγ)\alphax = exp\left({x}^{\beta}{y}^{\gamma}\right) be the solution of the differential equation 2x2ydy−(1−xy2)dx=02{x}^{2}ydy - \left(1 - x{y}^{2}\right)dx = 0, x>0,y(2)=log⁡e2x > 0, y\left(2\right) = \sqrt{\log_{e}2}. Then α+β−γ\alpha + \beta - \gamma equals :

Options

  1. A11
  2. B−1- 1
  3. C00
  4. D33

Correct answer

A. 11

Step-by-step solution

Given the solution of differential equation,

\alphax=exβ⋅yγ......(1)\alphax = {e}^{{x}^{\beta} \cdot {y}^{\gamma}} . . . . . . ( 1 )

Now calculating the solution of differential equation,

2x2ydydx=1−xy22{x}^{2}y\dfrac{dy}{dx} = 1 - x{y}^{2}

Let y2=t⇒2dydx=dtdx{y}^{2} = t ⇒ 2\dfrac{d y}{d x} = \dfrac{d t}{d x}

∴x2dtdx=1−xt∴ {x}^{2}\dfrac{dt}{dx} = 1 - xt

dtdx+tx=1x2.....(2)\dfrac{dt}{dx} + \dfrac{t}{x} = \dfrac{1}{{x}^{2}} . . . . . ( 2 )

Above differential equation is linear in tt

We know solutions of differential equation of the form dydx+Py=Q\dfrac{dy}{dx} + Py = Q is given by,

y.e∫Pdx=∫Q.e∫Pdx+C(e∫Pdx=I.F.)y . {e}^{∫ Pdx} = ∫ Q . {e}^{∫ Pdx} + C ( {e}^{∫ Pdx} = I . F . )

Now calculating, I.F.=e∫1xdx=eln⁡x=xI . F . = {e}^{∫ \dfrac{1}{x}dx} = {e}^{\ln x} = x

Therefore, the solution of equation (2)\left(2\right) is given by,

t.x=∫1x2⋅xdx+Ct . x = ∫ \dfrac{1}{{x}^{2}} \cdot xdx + C

⇒y2⋅x=ln⁡x+C⇒ {y}^{2} \cdot x = \ln x + C

∵y(2)=ln⁡2∵ y ( 2 ) = \sqrt{\ln 2}

∴2.ln⁡2=ln⁡2+C⇒C=ln⁡2∴ 2 . \ln 2 = \ln 2 + C ⇒ C = \ln 2

Hence, solution is xy2=ln⁡x+ln⁡2x{y}^{2} = \ln x + \ln 2

⇒xy2=ln⁡2x⇒ x{y}^{2} = \ln 2x

⇒2x=ex⋅y2......(3)⇒ 2x = {e}^{x \cdot {y}^{2}} . . . . . . ( 3 )

On comparing equations (1)\left(1\right) and (3)\left(3\right) we get,

α=2,β=1,γ=2\alpha = 2, \beta = 1, \gamma = 2

∴α+β−γ=1∴ \alpha + \beta - \gamma = 1

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