8. \( 3 \sin ^{3} t \csc t+\cos ^{2} t+2 \cos (-t) \cos t \)
\( 3\sin^2 t + \cos^2 t + 2\cos^2 t = 3\sin^2 t + 3\cos^2 t \)
Step 1 :\( 3\sin^3 t \csc t = 3\sin^2 t \)
Step 2 :\( 2\cos(-t)\cos t = 2\cos^2 t \)
Step 3 :\( 3\sin^2 t + \cos^2 t + 2\cos^2 t = 3\sin^2 t + 3\cos^2 t \)