[tex]\bf tan^2(x)-1=0\implies tan^2(x)=1\implies tan(x)=\pm\sqrt{1} \\\\\\ tan^{-1}[tan(x)]=tan^{-1}(\pm 1)\implies x=tan^{-1}(\pm 1)\implies x= \begin{cases} \frac{\pi }{4}\\\\ \frac{3\pi }{4}\\\\ \frac{5\pi }{4}\\\\ \frac{7\pi }{4} \end{cases}[/tex]
