7-2 The Pythagorean Theorem and Its Converse Goal 1: To use the Pythagorean Theorem Goal 2: To use the Converse of the Pythagorean Theorem

The well-known right triangle relationship called the Pythagorean Theorem is named for Pythagoras, a Greek mathematician who lived in the sixth century b.c. We now know that the Babylonians, Egyptians, and Chinese were aware of this relationship before its discovery by Pythagoras.

The Pythagorean Theorem In a right triangle, the sum of the squares of the lengths of the legs is equal to the square of the length of the hypotenuse.

A Pythagorean triple is a set of nonzero whole numbers a, b, and c that satisfy the equation a2 + b2 = c2. Here are some common Pythagorean triples. 3, 4, 5 5, 12, 13 8, 15, 17 7, 24, 25 If you multiply each number in a Pythagorean triple by the same whole number, the three numbers that result also form a Pythagorean triple.

You can use the Converse of the Pythagorean Theorem to determine whether a triangle is a right triangle.

Converse of the Pythagorean Theorem If the square of the length of one side of a triangle is equal to the sum of the squares of the lengths of the other two sides, then the triangle is a right triangle.

Theorem: If the square of the length of the longest side of a triangle is greater than the sum of the squares of the lengths of the other two sides, the triangle is obtuse. If c2 > a2 + b2, the triangle is obtuse.

Theorem: If the square of the length of the longest side of a triangle is less than the sum of the squares of the lengths of the other two sides, the triangle is acute. If c2 < a2 + b2, the triangle is acute.