cos(x+4)=cos x cos y-sin x sin y

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

If cos x.cos y + sin x.sin y = -1 then cos x + cos y is यदि cos x.cos y + sin x.sin y = -1 हो, तो cos x + cos y का मान क्या होगा?

If cos (x-y) =-1, then the values of (cos x+ cos y) and (sin x + sin y) are respectively-

If cos (x-y)+1=0, then the value of (cos x+ cos y) and (sin x+sin y) is-

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

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

cos4x-cos4y = 8 (cos x-cos y) (cos x + cos y) (cos x-sin y) (cos x + sin y)