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SSC CHSL 2024 · PYQ · Trigonometry · medium

What is the value of cos(x + y) – sin(x – y) + tan(2z)?

  1. A.cos x · cos y – sin x · sin y – cos x · sin y + tan z / (1 – tan² z)
  2. B.cos x · cos y – sin x · sin y – sin x · cos y – cos x · sin y + 2 tan z / (1 – tan² z)
  3. C.sin x · sin y + 2 tan z / (1 – tan² z)
  4. D.cos x · cos y – sin x · sin y – sin x · cos y + cos x · sin y + 2 tan z / (1 – tan² z)✓ Correct

Explanation

Expanding: cos(x+y) = cosx·cosy – sinx·siny; sin(x–y) = sinx·cosy – cosx·siny; tan(2z) = 2tanz/(1–tan²z). So the full expression equals cosx·cosy – sinx·siny – sinx·cosy + cosx·siny + 2tanz/(1–tan²z), which matches option (b).
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