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JEE Main20207 Jan 2020Evening ShiftMathematicsDefinite IntegrationActual

The value of α for which 4 α ∫ - 1 2 e - α x d x = 5 , is

Options

  1. Alog e 2
  2. Blog e 3 2
  3. Clog e 2
  4. Dlog e 4 3

Correct answer

A. log e 2

Step-by-step solution

4 α ∫ - 1 0 e α x d x + ∫ 0 2 e - α x d x = 5 ⇒ 4 α e α x α - 1 0 + e - α x - α ​ 0 2 = 5 ⇒ 4 α 1 - e - α α - e - 2 α - 1 α = 5 ⇒ 4 2 - e - α - e - 2 α = 5 Put e - α = t ⇒ 4 t 2 + 4 t - 3 = 0 ⇒ 2 t + 3 2 t - 1 = 0 ⇒ e - α = 1 2 ⇒ α = ln 2

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