[" 3.Prove that "1-],[qquad cos(x+y)=cos x cos y-sin x sin y]

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

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

Prove that: quad (cos x+cos y)^(2)+(sin x-sin y)^(2)=4cos^(2)(x+y)/(2)

Prove that: quad (cos x-cos y)^(2)+(sin x-sin y)^(2)=4sin^(2)(x-y)/(2)

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

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 that : (sin x - sin y)/(cos x + cos y) = tan ((x-y)/2)

Prove that : (sin x + sin y)/(cos x + cos y) = tan ((x+y)/2)