1.

If A + B = 90°, then express cos B in terms of simplest trigonometric ratio of A.

Answer»

Given: A + B = 90°

⇒ B = 90° - A

Multiplying both side by cos, we get

= cos B = Cos (90° - A)

⇒ cos B = sin A [∵ Sin θ = cos (90° - θ)]



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