Prove that Cos θ Sin (90° - θ) + Sin θ Cos (90° - θ) = 1

Prove that cos θ sin (90° - θ) + sin θ cos (90° - θ) = 1.

Sum

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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