$\begin{aligned}
& \sec ^2 x-\tan ^2 x=1 \quad(\text { on replacing } y \text { with } x) \
& \Rightarrow \text { Reflexive } \
& \sec ^2 x-\tan ^2 y=1 \
& \Rightarrow 1+\tan ^2 x+1-\sec ^2 y=1 \
& \Rightarrow \sec ^2 y-\tan ^2 x=1 \
& \Rightarrow \text { symmetric } \
& \sec ^2 x-\tan ^2 y=1 \
& \sec ^2 y-\tan ^2 z=1
\end{aligned}Addingboth\begin{aligned}
& \Rightarrow \sec ^2 x-\tan ^2 y+\sec ^2 y-\tan ^2 z=1+1 \
& \sec ^2 x+1-\tan ^2 z=2 \
& \sec ^2 x-\tan ^2 z=1 \
& \Rightarrow \text { Transitive }
\end{aligned}$ hence equivalence releation