5sinx2x-11sin^2 x+3=0 7cos2x-10sinx-3=0

7cos2x-10sinx-3=0 
7(cos^2x-sin^2x)-10sinxs-3=0
7(1-sin^2x)-10sinx-3=0
14sin^2x+10sinx-4=0
sinx=t
14t^2+10t-4=0
t1=-1    t2=2/7
sinx=-1   =>x=-pi/2+2pi n
sinx=2/7    =>x=(-1)^n arcsin2/7+pi n