Trigonometric Function

**MATNTRNG** · August 2nd 2010, 03:31 PM

The inverse of Cos x is a function. The domain of Cos x could be ???

How would I find the domain???

**Prove It** · August 2nd 2010, 04:11 PM

In order for $\textrm{Cos}\,{x}$ to have an inverse function, it must be one-to-one.

Draw the function $\cos{x}$ . Can you choose a domain where there aren't any repeating $y$ values?

**eumyang** · August 2nd 2010, 04:31 PM

Hmm... I'm assuming that the fact that C is capitalized is significant. I only learned $f(x) = \cos \,x$ when I was in school, and had never seen $f(x) = Cos \,x$ until now. Is it a regional/national thing? I'm in the US.

**Prove It** · August 2nd 2010, 04:34 PM

The capitalisation means there has been a standard restriction on the domain of $\cos{x}$ . It's up to you to find what that domain is.

Like I said, draw the function, and choose a domain in which there are not any repeating $y$ values.