Imagine zooming in on the graph as x slides toward a from the left and from the right. If the y-value heads to the same number L from both sides, that number is the limit. The function doesn't even have to be defined at a — limits care about what's happening near a, not at it.
Use whenever a free-response problem asks for a limit value. Try direct substitution first — only escalate to algebra or L'Hôpital if you hit an indeterminate form.
Evaluate the limit of 3x + 1 as x approaches 2.
- 1
The function 3x + 1 is a polynomial, so it's continuous everywhere — direct substitution works.
- 2
Substitute x = 2 into the expression.
- 3
Simplify.