cos2x=1-sin^2 x
Try that, I think you will get a quadratic equation
Solve for X:
5sinx+2cos2x-3=0
2 answers
5sinx+2cos^2x-2sin^x-3=0
5sinx+2-2sin^2x-2sin^2x-3=0
4sin^2x-5sinx+1=0
5sinx+2-2sin^2x-2sin^2x-3=0
4sin^2x-5sinx+1=0