1. A special triangle occurs if one of the interior angles is 90° . This is called a right triangle and can be created by choosing sides of lengths 3-4-5. Choosing sides of lengths 6-8-10 (doubling 3-4-5) or 9-12-15 (tripling 3-4-5) can also produce a right triangle.

Some other sets of three numbers that will produce a right angle triangle are 5-12-13, 7-24-25, and 9-40-41. There are ways to produce a right triangle where all the sides are not whole numbers.