Geometry · Points, Lines & Angles
Perpendicular
HSG-CO.A.1
Definition
Two lines, rays, or segments that intersect to form right angles.
Examples
- Perpendicular lines meet at a right angle (90 degrees), written AB perpendicular to CD.
- The two sides of a square meet perpendicular to each other.
Key rule
Perpendicular lines always cross at exactly 90 degrees.
Memory hook
Crosses like a plus sign — always at 90 degrees.