" Prove geometrically that "cos(x+y)=cos x cos y-sin x sin y

Prove geometrically that cos (x+y) =cosx cosy +sin x sin y

Prove geometrically that cos(x + y) = cos x cos y - sinx sin y and hence prove cos((pi)/(2) + x) = - sin x .

(a)Derive geometrically that cos(x+y)=cos x cos y-sin x sin y .Hence deduce the valueof cos 75^@

Prove that cos (x + y) = cos x cos y-sin x sin y

The value of (sin x cos y + cos x sin y)^2+(cos x cos y -sin x sin y)^2 is equal to

Prove the following: cos(x+y)cos(x-y)=cos^2y-sin^2x

Prove that, cos 4 x - cos4 y = 8(cos x - cos y)(cos x + cos y)(cos x - sin x)(cos x + sin y)