Hello,
I'm having a problem getting excel to calculate the angles of a triangle.

I know the formula for calculating angle C for instance (knowing lengths of
all three sides)

cosinus^-1 of (a^2+b^2-c^2)/(2*a*b)

But how do I put this into excel? When I put it in as following:
COS^1((a^2+b^2-c^2)/(2*a*b)) It dosn't work.

Can anybody help me?

Thanks