Help is appreciate it is for online Class and is very confusing ​

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?

What is the logarithmic function modeled by the following table? x f(x) 9 2 27 3 81 4

Can (2,3 and square root 10) be sides ona right triangle?