Question

How do you apply the double angle formula for `sin 8x cos 8x`?

Answer 1

Think about double angle formulas until you think of one that might be useful.

`sin 2 theta = 2 sin theta cos theta`

That looks helpful.

`2 sin theta cos theta = sin 2 theta`

so
`sin theta cos theta = 1/2 sin 2 theta`

And
`sin 8x cos 8x = 1/2 sin 16x`