Please clear my doubt. :/

$$\begin{gathered} \tan \theta \left[\begin{array}{cc}Sec\theta & \tan \theta \\ \tan \theta & -sec\theta \end{array}\right] + sec\theta \left[\begin{array}{cc}-\tan \theta & -sec\theta \\ -sec\theta & \tan \theta \end{array}\right] \\ Sol \\ \left[\begin{array}{cc}\tan \theta sec\theta & {\tan }^2\theta \\ {\tan }^2\theta & -\tan \theta sec\theta \end{array}\right] + \left[\begin{array}{cc}-\tan \theta sec\theta & -se{c}^2\theta \\ -se{c}^2\theta & \tan \theta sec\theta \end{array}\right] \\ = \left[\begin{array}{cc}0& {\tan }^2\theta - se{c}^2\theta \\ {\tan }^2\theta -se{c}^2\theta & 0\end{array}\right] \\ \left[\begin{array}{cc}Is {\tan }^2\theta -se{c}^2\theta = -1 ?& \\ if so .....how ?& \end{array}\right] \end{gathered}$$