If $f(x)$ is a function whose domain is $[-1,9]$, and $g(x)=f(x^2)$, then the domain of $g(x)$ is an interval of what width?
The minimum value of $x^2$ is $0$, the maximum is $81$. The answer is just $\boxed{81}$.
The answer is actually 6.
+148 
+605 
