Question

sin a*cos a(cos^2 a-sin^2 a)

Answer 1

$Sin\alpha Cos\alpha (Cos^{2}\alpha -Sin^{2} \alpha)=Sin\alpha Cos\alpha*Cos2\alpha=\frac{1}{2}*2Sin\alpha Cos\alpha*Cos2\alpha=\frac{1}{2}Sin2\alpha Cos2\alpha=\frac{1}{2}*\frac{1}{2}*2Sin2\alpha Cos2\alpha=\frac{1}{4}Sin4\alpha=0,25Sin4\alpha$