Slopes of parallel and perpendicular lines
MathDefinition
Parallel lines have the same slope but different y-intercepts. Perpendicular lines have slopes that are negative reciprocals of each other, meaning the product of their slopes is −1.
Examples
- y = 3x + 1 and y = 3x − 4 are parallel (both have slope 3)
- y = 2x + 1 and y = −½x + 3 are perpendicular (2 × −½ = −1)
Key Fact
Parallel: m₁ = m₂; Perpendicular: m₁ · m₂ = −1
Study This Concept
Practice slopes of parallel and perpendicular lines with free review games in these units: