can someone explain to me how arcsec infinity is equal to pi/2? thanks
Strictly speaking, " " isn't or any other number. " " 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. and as goes to , goes to 0 and so "goes to infinity" (get larger without bound). Thus, if we extend the real numbers sytem in that way, we have that " " and so " ".