2(1-sin^2 2x)+5sin2x-4=0
2-2sin^2(2x)+5sin2x-4=0
2sin^2(2x)-5sin2x+2=0
sin2x=t
2t^2-5t+2=0
|t|<=1</p>
t=1/2
sin2x=1/2
x=П/12+Пk k=1 13П/12
x=5П/12+Пk k=1 17П/12
5cos2x+7cos(x-3п/2)+1=0,при cos< или=0
5(cos^2x-sin^2x)+7cos(3П/2-x)+1=0
5-10sin^2x-7sinx+1=0
10sin^x+7sinx-6=0
sinx=1/2
x=5п/6+2Пk