# TrigonometryCircular Functions

#### CaptainBlack

##### Well-known member

The argument of $$\rm{asec}$$ is just a number so I don't see what $$\rm{rad}$$ is doing in your question.

CB

#### HallsofIvy

##### Well-known member
MHB Math Helper
-rad(2)? Do you mean "- 2 radians"? Use the fact that sec(x)= 1/cos(x) and use a calculator (making sure it is in "radian" mode) to find $$cos^{-1}(-1/2)$$.
Or do you mean "radical(2)" as in "$$\sqrt{2}$$"? $$\frac{1}{\sqrt{2}}= \frac{\sqrt{2}}{2}$$ so find $$cos^{-1}\left(-\frac{\sqrt{2}}{2}\right)$$. You shouldn't need a calculator for that.