18.44) (sin^2)2x-sin^2x=1/2

[latex]sin^22x=4sin^2xcos^2x=4sin^2x(1-sin^2x)=4sin^2x-4sin^4x\\8sin^4x-6sin^2x+1=0\\(2sin^2x-1)(2sinx-1)(2sinx+1)=0\\\\sinx=\pm{1\over2}\\cos(2x)=0\\\\x=\pm{\pi\over6}+\pi k, k\in Z\\x={\pi\over4}+{\pi k\over2},k\in Z[/latex]