## Algebra 2 (1st Edition)

$1-\tan^2 x$
Here, we have $\cos^2 x-\sin^2 x \ne 1$ Use the correct identity $\sin^2 x +\cos^2 x = 1$ or, $=1-\dfrac{\sin^2 x}{\cos^2 x}$ or, $=1-\tan^2 x$