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JEE Main202127 Jul 2021Morning ShiftMathematicsDifferential EquationsActual

Let y = y x be solution of the differential equation log e d y d x = 3 x + 4 y , with y 0 = 0 . If y - 2 3 log e 2 = α log e 2 , then the value of α is equal to:

Options

  1. A- 1 4
  2. B1 4
  3. C2
  4. D- 1 2

Correct answer

A. - 1 4

Step-by-step solution

Given, log e d y d x = 3 x + 4 y ⇒ d y d x = e 3 x · e 4 y ⇒ ∫ e - 4 y d y = ∫ e 3 x d x ⇒ e - 4 y - 4 = e 3 x 3 + C Given, y 0 = 0 So, - 1 4 - 1 3 = C ⇒ C = - 7 12 So, the particular solution is e - 4 y - 4 = e 3 x 3 - 7 12 ⇒ e - 4 y = 4 e 3 x - 7 - 3 ⇒ e 4 y = 3 7 - 4 e 3 x ⇒ 4 y = ln 3 7 - 4 e 3 x 4 y = ℓ n 3 6 when x = - 2 3 ℓ n 2 ⇒ y = 1 4 ℓ n 1 2 ⇒ y = - 1 4 ℓ n 2 So, α = - 1 4

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