Question

Please solve this for me.

Answer 1

$\cos(4x) = 1 - 2 { \sin(2x) }^{2} \\ = 1 - 2{(2 \sin(x) \cos(x) ) }^{2} \\ 1 - 8 { \sin(x) }^{2} . { \cos(x) }^{2}$
hence proved......