Hello,

You want to go from exponentials to sines.

So you should remember this formula :

but here, you have things like

so try to see what happens if you multiply the sine formula by , to get 1 on the right side :

and finally,

which is equivalent to (t=2x)

Applying this to the formula you have :

note that 2i can be simplified :

now using simple property of exponents, we have

and this finishes the problem :P