Explain why direct substitution in as gives an indeterminate form

MATHEMATICS · Subjective · AP · Calculus AB · Limits and Continuity · Limits and Continuity

Problem

Explain why direct substitution in

\displaystyle \frac{x^{2}-9}{x-3}

x \to 3

gives an indeterminate form, and state the common factor that must be cancelled before evaluating the limit.