Question

what is sec(-π/2)?

Answer 1

\[\sec (x)= \frac{1}{\cos x}\]
we know
\[\cos (\frac{\pi}{2})=\cos (\frac{-\pi}{2})= 0\]
so
\[ \sec ( -\frac{\pi}{2})= \frac{1}{\cos \pi/2}= 1/0= \infty\ or\\ not\ defined\]