Resposta:
[tex]cos^2x-sen^2x=0[/tex]
[tex]cos2x=0[/tex]
[tex]2x=arccos(0)\\[/tex]
[tex]2x= (2k+1)\frac{\pi}{2}[/tex]
[tex]x= \frac{1}{2} (2k+1)\frac{\pi}{2}[/tex]
[tex]x= (2k+1)\frac{\pi}{4}[/tex]
[tex]x= k\frac{\pi}{2} +\frac{\pi}{4},\ \ \ k \in Z\\[/tex]
