cos y=x cos(a+y)

If cos x + cos y- cos(x +y) = 3/2 then x=y is possible.

If cos y=x cos(alpha-y) then (1+x^(2)-2x cos alpha)*(dy)/(dx) is (A) sin alpha (B) -sin alpha (C) cos alpha (D) -cos alpha

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 (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)

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)

cos ^(-1) ""((cos x + cos y)/(1+cos x cos y))= 2 tan ^(-1) (tan ""(x)/(2) tan ""(y)/(2))

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

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

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

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