This picture suggests a relationship between the lengths, A, B, and C, which you may recognize as the "Pythagorean Theorem." Despite having his name attached to this idea, special cases were known in ancient Mesopotamia, Egypt, and India more than a thousand years before Pythagoras discovered it in Greece around 500 BC, and diagrams (like the one above) explaining this relationship also appear in Chinese texts near the same time. 

The independent discoveries of " A2 + B2 = C2 " by people in totally different cultures and regions of the world is important because (1) there must be something elemental about this statement and (2) all these people were applying math to solve real-world problems! Today, this equation allows us to compute distances in a coordinate system, and without it, modern computer graphics wouldn’t exist.