Hi I am not sure what to do with this one

Evaluate the following integral

definite integral sign b="a" ; a=0 ( x )* ("a"^2 - x^2)^1/2 dx

where "a" is a positive constant

I know the x must be x^2 on the other side but I really don't know what to do with this mess.

Directions please

This calculus beginner