Question #N568
The equation $\frac{x^2 + 3x}{x^2 - 9}$ is undefined when $x$ is equal to which of the following?
A. -3 only
B. 3 only
C. -3 or 3
D. 0, -3, or 3
Correct Answer is: C
A rational expression is undefined when the denominator is equal to zero. Factoring the denominator, we get $x^2 - 9 = (x+3)(x-3)$. This expression equals zero when $x = -3$ or $x = 3$. Therefore, the expression is undefined when $x = -3$ or $x = 3$.