A worked example
The points (1, 2) and (4, 8) give a slope of exactly 2, with the line equation y = 2x.
Frequently asked questions
What does a negative slope mean?
The line goes downward as you move from left to right — y decreases as x increases. A positive slope means the line rises left to right.
What does a slope of 0 mean?
The line is perfectly horizontal — y stays the same no matter what x is.
Why is a vertical line's slope undefined rather than infinite?
Slope is rise over run — for a vertical line, the run (change in x) is zero, and division by zero is undefined, not a number (even a very large one).