How it works
Slope measures steepness: how much y changes for each one-unit change in x. It is "rise over run" between two points on the line.
A positive slope rises to the right, a negative slope falls, a zero slope is horizontal, and a vertical line has an undefined slope because the run is zero.
From the slope and one point, the calculator writes the line's equation in slope-intercept form (y = mx + b), point-slope form, and (for whole-number points) standard form Ax + By = C.
Formula
m = (y₂ − y₁) ÷ (x₂ − x₁); b = y₁ − m·x₁
Questions people ask
What is the slope of a horizontal line?
Zero, because y does not change. Its equation is y = constant.
How is slope related to angle?
Slope equals the tangent of the angle the line makes with the x-axis. A slope of 1 is 45°.
How do I know if two lines are parallel or perpendicular?
Parallel lines have equal slopes. Perpendicular lines have slopes whose product is −1, such as 2 and −1/2.