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The number of ordered pairs x , y of real numbers satisfying the system of equations sin ⁡ x = sin ⁡ 2 y and cos ⁡ x = sin ⁡ y , where 0 ≤ x , y ≤ π , is

Options

  1. A1
  2. B2
  3. C3
  4. D4

Correct answer

B. 2

Step-by-step solution

sin ⁡ x = sin ⁡ 2 y and cos ⁡ x = sin ⁡ y Squaring and adding, we get, 1 = 2 sin ⁡ y cos ⁡ y 2 + sin 2 ⁡ y 1 - sin 2 ⁡ y = 4 sin 2 ⁡ y cos 2 ⁡ y cos 2 ⁡ y 1 - 4 sin 2 ⁡ y = 0 cos ⁡ y = 0 or sin ⁡ y = ± 1 2 y = π 2 or π 6 or 5 π 6 y = π 2 ⇒ x = 0 y = π 6 ⇒ x = π 3 ⇒ two ordered pairs 0 , π 2   &   π 3 , π 6

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