`(cos x- cos y) ^(2) + (sin x - sin y) ^(2) =4 sin ^(2) "" ( x-y)/(2)`

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

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

cos x + cos y + cos z = 0 and sin x + sin y + sin z, then cos ^(2) (( x-y)/( 2)) =

If cos x+ cos y = 1//3 , sin x + sin y=1//4 " then " cos (x+y)=

If y= ( sin^(4) x - cos^(4) x + sin^(2) x cos^(2) x )/( sin^(4) x + cos^(4) x + sin^(2) x cos^(2) x) , x in ( 0, (pi)/(2) ) , then

If y =a cos 2x +b sin 2x then y _(2) + 4y =

sin 3x + sin 2x - sin = 4sin x cos "" x/2 cos "" (3x)/(2)