# Math Help - question on arcsec infinity

1. ## question on arcsec infinity

can someone explain to me how arcsec infinity is equal to pi/2? thanks

2. Originally Posted by FailCalculus
can someone explain to me how arcsec infinity is equal to pi/2? thanks
$\sec \theta=\frac{1}{\cos \theta}$

Set the denominator to be 0

3. Originally Posted by FailCalculus
can someone explain to me how arcsec infinity is equal to pi/2? thanks
Strictly speaking, " $arcsec(\infty)$" isn't $\pi/2$ or any other number. " $\infty$" isn't a number so secant is not defined for it. You could, of course, extend the real number system to include "infinities" but there are several different ways to do that- you would have to specify which you meant.

But, we can talk about this in the limit sense. $sec(\theta)= \frac{1}{cos(\theta)}$ and as $\theta$ goes to $\pi/2$, $cos(\theta)$ goes to 0 and so $sec(\theta)= \frac{1}{cos(\theta)$ "goes to infinity" (get larger without bound). Thus, if we extend the real numbers sytem in that way, we have that " $sec(\pi/2)= \infty$" and so " $arcsec(\infty)= \pi/2$".