Parallel and perpendicular lines
MathDefinition
Parallel lines have the same slope and never intersect. Perpendicular lines intersect at right angles (90°) and have slopes that are negative reciprocals of each other.
Examples
- y = 2x + 1 and y = 2x - 3 are parallel (both have slope 2)
- y = 2x + 1 and y = -½x + 4 are perpendicular (slopes 2 and -½)
- Railroad tracks are parallel lines; a street crossing them is perpendicular
Key Fact
Parallel: m₁ = m₂; Perpendicular: m₁ × m₂ = -1
Study This Concept
Practice parallel and perpendicular lines with free review games in these units: