Question

Find the value of cos θ cos (90 –θ ) – sin θ sin (90 – θ).

Answer 1

Trigonometry is the study of the relationship between the sides and angles of a triangle.

Two angles are said to be complementary of their sum is equal to 90° .
θ & (90° - θ) are complementary angles.

SOLUTION:

Given:
cos θ cos (90 –θ ) – sin θ sin (90 – θ)
= cos θ sin θ  – sin θ cos θ = 0

[ cos (90-θ)] = Sin θ , sin (90-θ)] = cos θ]

cos θ cos (90 –θ ) – sin θ sin (90 – θ) = 0

Hence, the value of cos θ cos (90 –θ ) – sin θ sin (90 – θ) is 0 (zero).

HOPE THIS WILL HELP YOU..

Answer 2

it's value is Zero ( 0 ) ....
by using identity of cos(90-x) = sinx and sin(90-x) = cos x
we get , cosx.cos(90-x) - sinx.sin(90-x)
= cosx.sinx - sinx.cosx
= 0