Ok, I just discovered that I am not allowed to use a calculator on my exam.

Now, I have no idea how to calculate roots and sin and cos values manually. And my textbook does not say.

So. If I am left with this:

Cos-1(-4/(sqrt(11)sqrt(14))) how can I solve this?

(I understand that this is not a place to provide a complete explanation so a hint to what I can google for or a website link will be enough to get me started)

Any help is appreciated.

I tried to google a little for myself but I did not find a relatively simple explanation)