prove that: `cos^2x+cos^2y-2cosx*cosy*cos(x+y)=sin^2(x+y)`

prove that: cos ^ (2) x + cos ^ (2) y-2cos x * cos y * cos (x + y) = sin ^ (2) (x + y)

prove that: (sin2x-sin2y)/(cos2y-cos2x)=cot(x+y)

56.The value of cos^(2)x+cos^(2)y-2cos x cos y cos(x+y) is (A) sin(x+y) (B) sin^(2)(x+y) (C) sin(x+y) (D) sin(x+y)

Prove that : cosx+cosy+cosz+cos(x+y+z)=4cos((x+y)/(2))cos((y+z)/(2))cos((z+x)/(2))

Prove that (i) 2 cos x cos y=cos (x+y)+cos (x-y) (ii) -2 . sin x sin y=cos (x+y)-cos (x-y) (iii) 2 sin x cos y=sin (x+y)+sin (x-y) (iv) 2 cos x sin y=sin (x+y)-sin (x-y)

Prove that: (cosx+cosy)^2+(sinx-siny)^2 =4cos^2 (x+y)/2

Prove that (cosx +cosy)^2+(sinx+siny)^2=4cos^2((x-y)/2)

Prove that : (cosx+cosy)^(2)+(sinx-siny)^(2)=4cos^(2)""(x+y)/(2)

Prove that (cosx+cosy)^2+(sinx-siny)^2=4cos^2((x+y)/2)

If cosx+cosy-cos(x+y)=(3)/(2) then