Simplifying ln(exp(-a) + exp(a)) - Need Help with Homework

[Kat007]

Homework Statement

Hey, does anyone know how to further simplify this:

Homework Equations

ln(exp(-a) + exp(a))?

The Attempt at a Solution

 

[rock.freak667]

There is no such rule as ln(x+y)=lx+lny if that is what you wanted to know. The most I can think of is that cosh(x)= 1/2(e^x+e^-x)

 

[Kat007]

Thank you, this is good. I was after a trig simplification.
I knew one for 2cos(x) = exp(-ix) + exp(ix) but couldn't remember one without the imaginary.
Ta!