## Algebra and Trigonometry 10th Edition

The identity is verified. The graph of $f(y)=cot^2y(sec^2y-1)$
$1+tan^2y=sec^2y$ $tan^2y=sec^2y-1$ $cot^2y(sec^2y-1)=cot^2y~tan^2y=\frac{1}{tan^2y}·tan^2y=1$