Answer
$-2$
Work Step by Step
Note that $\sec x=\frac{1}{\cos x}$ and $\csc x=\frac{1}{\sin x}$
We use the unit circle values to simplify.
Since $\cos{\pi}=-1$ and $\sin{\frac{\pi}{2}}=1$, then
$\sec \pi - \csc \frac{\pi}{2}\\
= \dfrac{1}{ \cos (\pi)} - \dfrac{1}{ \sin (\pi/2)} \\
=\frac{1}{-1}-\frac{1}{1}\\
=-1 -1 \\= -2$
