In the right triangle ABC, the angle C is a right angle. If CD is perpendicular to AB, the square of CD is equal to AD times BD.

The square of AC is equal to AB times AD.

The square of BC is equal to AB times DB.

For a right-angled triangle, if A, B and C are used to represent the vertices of the triangle, where A is the right-angled vertex, and the intersection of the vertical line BC with the vertical foot with point A as the hypotenuse is D, then there is AD 2 = BD * CD. (AD is the proportional average of BD CD).

This is the projective theorem, and the proof is brief. But it should be noted that there is no projective theorem for general triangles! So, this is one of the properties of right triangle.

As for who invented it, I don't know