AP Calculus AB and BC glossary
Direct substitution
Direct substitution evaluates a limit by putting the value straight into the function. It is valid exactly when the function is continuous at that point, which makes it the first thing to try on any limit.
If substitution gives a number, that number is the limit and you are finished. If it gives an indeterminate form, the attempt has told you which technique to reach for next rather than wasted your time.
A result like is not indeterminate: it means the limit is infinite, so check the one-sided behaviour to determine the sign.
Appears in: Unit 1: Limits and Continuity