Reorder 2 cos (2y) and sin (2y)
= sin (2y)(2 cos(2y))
Remove parenthesis
= sin (2y) * 2 cos (2y)
Reorder sin (2y) and 2
= 2 * sin (2y) cos (2y)
Apply the sine double-angle identity
= sin (2(2y))
Now multiply 2 by 2
= sin (4y)
