The expression simplifies to:

( (1+\tan^2\alpha)\cos^2\alpha - 1 )

Since ( \tan^2\alpha = \frac{\sin^2\alpha}{\cos^2\alpha} ) and ( \sin^2\alpha + \cos^2\alpha = 1 ), we can rewrite the expression as:

( (\frac{\sin^2\alpha}{\cos^2\alpha} + 1)\cos^2\alpha - 1 )

Simplify further:

( \frac{\sin^2\alpha + \cos^2\alpha}{\cos^2\alpha}\cos^2\alpha - 1 )

( \sin^2\alpha - 1 )

So, the final simplified expression is ( \sin^2\alpha - 1 ).