Geometry · Coordinate Geometry
Perpendicular Slopes
HSG-GPE.B.5
Definition
Perpendicular lines have slopes that are negative reciprocals of each other.
Examples
- Slopes of 2 and -1/2 are negative reciprocals, so the lines are perpendicular.
- Slopes of 3 and -1/3 are negative reciprocals, so the lines are perpendicular.
Key rule
Two slopes multiply to -1 exactly when the lines are perpendicular.
Memory hook
Flip and negate the slope to find the perpendicular one.