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Question
Prove that cos θ sin (90° - θ) + sin θ cos (90° - θ) = 1.
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Solution
LHS = cos θ sin (90° - θ) + sin θ cos (90° - θ)
= cos θ. cos θ + sin θ. sin θ
= cos2θ + sin 2θ
= 1
= RHS
Hence proved.
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