2cos2x=1-7sinx-2cos2x

I cannot get past this:

2cos2x+2cos2x=1-7sinx
4cos2x=

sorry pressed eneter

4cos2x=1-7sinx

Recall that cos2x = 1 - 2 sin^2x. Now you have a quadratic and can solve for sinx.

And lastly for 'x'.