Question

1-2sin2a +cos(4a-2π)​

Answer 1

$1-2Sin^{2} \alpha + Cos(4\alpha -2\pi ) = Cos2\alpha+ Cos4\alpha=2Cos\frac{2\alpha+4\alpha}{2} Cos\frac{2\alpha-4\alpha}{2} =\\\\=2Cos3\alpha Cos \alpha$