2cos2ysin2y

simplify

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)