Geometry · Triangles & Congruence
Altitude of a Triangle
HSG-CO.C.10
Definition
A perpendicular segment from a vertex to the line containing the opposite side.
Examples
- The altitude from vertex A is perpendicular to side BC — it's the triangle's height.
- Every triangle has three altitudes, one from each vertex.
Key rule
An altitude always meets the opposite side at a right angle.
Memory hook
The triangle's height — straight down, at 90 degrees.