Question

How do you evaluate $\sec (90°)$?

Answer 1

Finding the required value:

Since, $\sec \left(\mathrm{\theta }\right)=\frac{1}{\cos \left(\mathrm{\theta }\right)}$

$\sec (90°)=\frac{1}{\cos (90°)}$

$\sec (90°)=\frac{1}{0}$ $\left[\because \cos (90°)=0\right]$

As we know, $\frac{1}{0}$ is undefined.

Hence, $\sec (90°)$ is undefined.