The given expression can be proved using the Pythagorean identity as shown below:
[tex]L.H.S \\ \\
= 1+ sec^{2} *sin^{2}x \\ \\
=1+ \frac{1}{cos^{2}x } sin^{2}x \\ \\
=1+tan^{2}x \\ \\
=sec^{2}x \\ \\
= R.H.S
[/tex]
Thus, the Left hand side has been proved equal to Right Hand Side.