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JEE Main20211 Sep 2021Evening ShiftMathematicsDifferential EquationsActual

If y = y ( x ) is the solution curve of the differential equation x 2 d y + y - 1 x d x = 0 ; x > 0 and y ( 1 ) = 1 , then y 1 2 is equal to :

Options

  1. A3 + e
  2. B3 - e
  3. C3 2 - 1 e
  4. D3 + 1 e

Correct answer

B. 3 - e

Step-by-step solution

x 2 d y + y d x = d x x ⇒ d y d x + y x 2 = 1 x 3 I . F = e ∫ 1 x 2 d x = e - 1 x ⇒ y · e - 1 x = ∫ e - 1 x · 1 x 3 d x + C  Let  - 1 x = t ⇒ 1 x 2 d x = d t ⇒ y · e - 1 x = ∫ - t e t · d t + C = - t e t - e t + C ⇒ y · e - 1 x = 1 x e - 1 x + e - 1 x + C  Put  x = 1 ⇒ ( 1 ) · e - 1 = e - 1 1 + e - 1 + C ⇒ C = - e - 1 Equation is y · e - 1 x = 1 x e - 1 x + e - 1 x - e - 1 ⇒ y = 1 x + 1 - e 1 x e

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