15. Rational Expressions and Equations

For which of the following values of $x$ is the rational expression undefined?

$\frac{5}{x}$

For which of the following values of $x$ is the rational expression undefined?

$\frac{7}{x-3}$

For which of the following values of $x$ is the rational expression undefined?

$\frac{x+1}{x^2-9}$

Evaluate the rational expression below at $x=-1$.

$\frac{12}{x+3}$