Prove that geometrically that `cos (x+y)= cosx.cosy-sinx.siny` and hence show that `cos2x=cos^2x-sin^2x`.

Prove geometrically that cos (x+y) =cosx cosy +sin x sin y

Prove Geometrically cos(x+y)=cosx,cosy-sinx.siny and hence prove that cos(x-y)= cosxcosy+sinxsiny using unit circle concept ?

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

(a)Derive geometrically that cos(x+y)=cos x cos y-sin x sin y .Hence deduce the valueof cos 75^@

To cos(A+B)=cosx.cosy - sin x sin "and hence find "cos75^(@)

Prove that: cos3x=4cos^(3)x-3cosx

Prove that cos (pi/2 + x) = - sin x .

Prove that cos^(2)2x-cos^(2)6x=sin4x.sin8x ?