The mathematical theorem that in a right triangle, the square of the hypotenuse equals the sum of the squares of the other two sides. Commonly taught in Japanese junior high school mathematics.
See also: ピタゴラスの定理
Using the Pythagorean theorem, we find the length of the hypotenuse of the right triangle.
Synonymous; ピタゴラスの定理 is the direct loan from English and is also common, but 三平方の定理 is the native Japanese term often preferred in school textbooks.
From 三 (three) + 平方 (square) + の (possessive particle) + 定理 (theorem), literally 'theorem of three squares', referring to the three squares constructed on the sides of a right triangle.