Note the following nomenclature in the context of a right-angled triangle:
In the above figure, the side labeled $b$ is the hypotenuse.
In the above figure, the adjacent to vertex $A$ is side $c$.
In the above figure, the opposite to vertex $A$ is side $a$.
Also known as
A right-angled triangle is also often referred to as a right triangle.
In the words of Euclid:
- Further, of trilateral figures, a right-angled triangle is that which has a right angle, an obtuse-angled triangle that which has an obtuse angle, and an acute-angled triangle that which has its three angles acute.