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JEE Main 202125 FebruaryMorning Shift
Exam
JEE Main
Year
2021
Date
25 February
Shift
Morning Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2021 · 25 February · Morning Shift · Mathematics · Differential Equations

If a curve passes through the origin and the slope of the tangent...

If a curve passes through the origin and the slope of the tangent to it at any point (x,y)\left(x, y\right) is x2−4x+y+8x−2,\dfrac{{x}^{2} - 4x + y + 8}{x - 2}, then this curve also passes through the point:

Options

  1. A(5,4)\left(5, 4\right)
  2. B(4,4)\left(4, 4\right)
  3. C(4,5)\left(4, 5\right)
  4. D(5,5)\left(5, 5\right)

Correct answer

D. (5,5)\left(5, 5\right)

Step-by-step solution

Given

y(0)=0y\left(0\right) = 0

and dydx=(x−2)2+y+4x−2\dfrac{dy}{dx} = \dfrac{{\left(x - 2\right)}^{2} + y + 4}{x - 2}

⇒dydx−yx−2=(x−2)+4x−2⇒ \dfrac{dy}{dx} - \dfrac{y}{x - 2} = \left(x - 2\right) + \dfrac{4}{x - 2}

⇒I.F.=e−∫1x−2dx=1x−2⇒ I . F . = {e}^{- ∫ \dfrac{1}{x - 2}dx} = \dfrac{1}{x - 2}

Solution of L.D.E.

⇒y1x−2=∫1x−2((x−2)+4x−2)⋅dx⇒ y\dfrac{1}{x - 2} = ∫ \dfrac{1}{x - 2}\left(\left(x - 2\right) + \dfrac{4}{x - 2}\right) \cdot dx

⇒yx−2=x−4x−2+C⇒ \dfrac{y}{x - 2} = x - \dfrac{4}{x - 2} + C

Now, at x=0,y=0⇒C=−2x = 0, y = 0 ⇒ C = - 2

y=x(x−2)−4−2(x−2)y = x\left(x - 2\right) - 4 - 2\left(x - 2\right)

⇒y=x2−4x⇒ y = {x}^{2} - 4x

This curve passes through \left(5, 5\right)$

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