The 3-4-5 Triangle. It is perhaps surprising that there are some right-angled triangles where all three sides are whole numbers called Pythagorean Triangles. The three whole number side-lengths are called a Pythagorean triple or triad. An example is a = 3, b = 4 and h = 5, called the 3-4-5 triangle. We can check it as follows: 3 2 +4 2 = 9 + 16 = 25 = 5 2 so a2 + b2 = h2. This triple was known to the Babylonians (who lived in the area of present-day Iraq and Iran) even as long as 5000 years ago! Perhaps they used it to make a right-angled triangle so they could make true right-angles when constructing buildings-we do not know for certain.