Question

a) cos² ⁡(α +x) +cos2² x - 2 cosα cosx.cos⁡(α +x);

b) sin⁡4x.sin⁡10x-sin⁡11x.sin⁡3x-sin⁡7x.sinx

Answer 1

b: =1/2*[cos(10x-4x)-cos(10x+4x)]-1/2*[cos(11x-3x)-cos(11x+3x)]-1/2*[cos(7x-x)-cos(7x+x)]

=1/2*[cos 6x-cos14x-cos8x+cos14x-cos6x+cos8x]

=0