For triangles that are not right-angled, the base is one of the sides and the perpendicular height may be shown either inside or outside the shape, it is not another side.

There are only two requirements for a right triangle. First, it has to be a shape with three sides---the "triangle" part. Second, one of the angles must be 90 degrees. That's it.

a ² + b ² = c ² Isosceles triangles can be split into two right-angled triangles. This means Pythagoras’ theorem can be used to find the lengths of missing sides, such as the perpendicular ...