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Given that \(\cos x + \cos y = 1\), the range of \(\sin x - \sin y\) is

Question and options

Given that cos⁡x+cos⁡y=1\cos x + \cos y = 1, the range of sin⁡x−sin⁡y\sin x - \sin y is
  1. [−1,1][-1, 1]
  2. [−2,2][-2, 2]
  3. [0,3][0, \sqrt{3}]
  4. [−3,3][-\sqrt{3}, \sqrt{3}]

Answer and explanation

Correct answer: D - \([-\sqrt{3}, \sqrt{3}]\)
(cos x + cos y)^2 + (sin x - sin y)^2 = 2 + 2cos(x+y), so (sin x - sin y)^2 = 1 + 2cos(x+y) <= 3. Attained at x = 60, y = -60 degrees (gives sqrt3) and symmetrically; range [-sqrt3, sqrt3].

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