Преобразуйте выражение

Решите задачу:

$cos^{2} x-sin( \frac{ \pi }{6} -x)sin (\frac{ \pi }{6} +x)= \\\ =cos^{2} x-0,5(cos(\frac{ \pi }{6} -x-\frac{ \pi }{6} -x)-cos(\frac{ \pi }{6} -x+\frac{ \pi }{6} +x))= \\\ =cos^{2} x-0,5(cos2x-cos\frac{ \pi }{3})=cos^{2} x-0,5(cos2x-0.5)= \\\ =cos^{2} x-0,5cos2x+0.25=cos^{2} x-0,5cos^2x+0.5sin^2x+0.25= \\\ =0,5cos^2x+0.5sin^2x+0.25=0.5+0.25=0.75$