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.
Read more about Right Triangle: Terminology, Characterizations, Trigonometric Ratios, Special Right Triangles, Thales' Theorem, Medians, Relation To Various Means and The Golden Ratio, Other Properties