An altitude in a triangle is a line segment from a vertex to the opposite side that is perpendicular to that side.

In this diagram, the dashed line segments show the altitude of each triangle.

A dilation is a transformation that can reduce or enlarge a figure.

A dilation with center and positive scale factor takes a point along the ray  to another point whose distance is times farther away from than is.

Triangle  is the result of applying a dilation with center and scale factor 3 to triangle .