1.

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

Answer»

Given: X + Y = 90°

⇒ X= 90° - Y

Multiplying both side by cos, we get

= cos X = Cos (90° - Y)

⇒ cos X = sin Y [∵ Sin θ = cos (90° - θ)]



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