How do i simplify the radical: square root of 324

One expression below in undefined, and the other expression has a well defined value. which expression is undefined and explain why it has no value. which expression is defined? what is the value of that expression and how do you know? what is a different expression using a trig inverse function that is also undefined?

Which expression is equivalent to 3^3 + 2^2?

We just started the introduction into circles and i have no idea how to do this.