[tex]sin ^2 2x - 2sin^2( x+ \frac{\pi}{2} ) + \frac{3}{4} = 0\\\Leftrightarrow sin ^2 2x-2cos^2x+\frac{3}{4}=0\\\Leftrightarrow sin ^2 2x-2cos^2x+1-\frac{1}{4}=0\\\Leftrightarrow sin^22x-cos2x-\frac{1}{4}=0\\\Leftrightarrow cos^22x+cos2x-\frac{3}{4}=0\\\Leftrightarrow ...[/tex]