Any Side Can Be the Base

Part of the Triangles section of Coddy's Geometry journey. Lesson 27 of 71.

Any side can be the base, as long as the height is measured to that side. Turn the triangle so a different side is at the bottom. The height changes with it, but the area, half of the base times the height, comes out the same.

$The same triangle drawn twice, once with its bottom side as the base and once with a slanted side as the base, each with its own perpendicular height$

The same triangle with two choices of base

A figure usually shows one height. The base is the side that the height meets at a right angle. Pairing a height with the wrong side gives the wrong area. In a right triangle the easiest pair is the two legs. The hypotenuse can be the base too, but then the height is the perpendicular drawn to it from the right angle.