what is an altitude of a triangle
The perpendicular from a vertex to the opposite side. Try this Drag the orange dots on each vertex to reshape the triangle. Note the position of the altitude as you drag. The altitude of a triangle is a line from a vertex to the opposite side, that is perpendicular to that side, as shown in the animation above. A triangle therefore has three possible altitudes. The altitude is the shortest distance from a vertex to its opposite side. It can refer to the line itself.