• In a right-angled triangle, the square of the hypotenuse equals the sum of the squares of the other two sides.
• The hypotenuse is the side opposite the right angle, and it is the longest side of the triangle.
• If we denote the hypotenuse by c and the other two sides by a and b, then:

c2 = a2 + b2

• From this relation, the hypotenuse is c = √(a² + b²), and a leg is a = √(c² − b²).
• Whole-number sets that satisfy the theorem are called Pythagorean triples, such as (3, 4, 5), (5, 12, 13) and (7, 24, 25).