<P> A right triangle (American English) or right - angled triangle (British English) is a triangle in which one angle is a right angle (that is, a 90 - degree angle). The relation between the sides and angles of a right triangle is the basis for trigonometry . </P> <P> The side opposite the right angle is called the hypotenuse (side c in the figure). The sides adjacent to the right angle are called legs (or catheti, singular: cathetus). Side a may be identified as the side adjacent to angle B and opposed to (or opposite) angle A, while side b is the side adjacent to angle A and opposed to angle B . </P>

What kind of triangle has a 90 degree angle