Press the Submit button to see if you are correct. Choose the sentence in this excerpt that defines the relationships expressed in the Pythagorean theorem. The Pythagorean Theorem, attributed to the 5th-century B.C.E. Greek mathematician and philosopher Pythagorus, expresses a relationship between the sides of a right triangle. In a right triangle, the square of the length of the hypotenuse equals the sum of the squares of the lengths of the other two sides. A practical application of this occurs on a baseball field. It's common knowledge that the shortest distance between two points is a straight line; therefore, the baseline logically represents the quickest path from the batter's box to first base.