Answer
$0$
Work Step by Step
We know that $\cos$ has a period of $ 2 \pi$ or $360^\circ$, so we can write $\cos{\theta}=\cos{(\theta-2\pi)}$
This implies that
$\cos{540^\circ}=\cos{(540^\circ-360^\circ)}=\cos{180^\circ}$
Since the trigonometric function $\tan$ is an odd function, we can write
$f(-\theta)=-f(\theta) \implies \tan{-45^\circ}=-\tan{45^\circ}$.
Therefore, $\cos{540^\circ}-\tan{-45^\circ}=\cos{180^\circ}+\tan{45^\circ} \\=-1+1\\=0$
