Assuming your problem is: 4cos^2x=sin^2x+34cos2x=sin2x+3
Using sin^2x+cos^2x=1sin2x+cos2x=1, we get
4(1-sin^2x)=sin^2x+34(1−sin2x)=sin2x+3
4-4sin^2x=sin^2x+34−4sin2x=sin2x+3
5sin^2x=15sin2x=1
sin^2x=0.2sin2x=0.2
=> sinx = sqrt0.2 = sqrt5 / 5 ⇒sinx=√0.2=√55
x=color(red)(sin^-1(sqrt5 / 5 )~~0.4647x=sin−1(√55)≈0.4647 color(red)(radrad