`If cos x + cos y = 2, "then the value of" sin(x + y) is-`

If cos x + cos y =2 , then the value of sinx + sin y is

If cos x + cos y =2, then value of sin x + sin y is

If sin x + sin y = a , cos x - cos y = b then the value of tan ((y-x)/2) is _______ in terms of a and b.

If sin x + sin y = a, cos x + cos y = b, then what is the value of cos (x-y) ?

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

If (sinx + sin y ) = a and (cos x + cos y ) = b what is the value of sin x sin y + cos x cos y ?

If cos x = tan y , cos y = tan z , cos z = tan x , then the value of sin x is :

Suppose that 'a' is a non-zero real number for which sin x+sin y=a and cos x + cos y= 2a . The value of cos(x-y) is

Suppose that 'a' is a non-zero real number for which sin x+sin y=a and cos x + cos y= 2a . The value of cos(x-y) is