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JEE Main201910 Apr 2019Morning ShiftMathematicsTrigonometric EquationsActual

All the pairs ( x , y ) , that satisfy the inequality 2 s i n 2 x - 2 s i n x + 5 · 1 4 s i n 2 y ≤ 1 also satisfy the equation:

Options

  1. A2 sin x = sin y
  2. Bsin x = 2 sin y
  3. Csin x = sin y
  4. D2 sin x = 3 sin y

Correct answer

C. sin x = sin y

Step-by-step solution

Given inequality is 2 sin 2 ⁡ x - 2 sin ⁡ x + 5   ≤ 4 sin 2 ⁡ y ⇒ sin 2 ⁡ x - 2 sin ⁡ x + 1 + 4 ≤ 2 sin 2 ⁡ y ⇒ sin ⁡ x - 1 2 + 4 ≤ 2 sin 2 ⁡ y ∵ 2 sin 2 ⁡ y ∈ 0 ,   2     &     sin ⁡ x - 1 2 + 4 ∈ 2 ,   2 2 ∵   Only equality holds ⇒ sin ⁡ x - 1 2 + 4 = 2 sin 2 ⁡ y = 2 ⇒ sin ⁡ x - 1 2 + 4 = 4 sin 4 ⁡ y = 4   ⇒ sin

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