Inverse Pythagorean theorem

In geometry, the inverse Pythagorean theorem is as follows:

Let A, B be the endpoints of the hypotenuse of a right triangle ABC. Let D be the foot of a perpendicular dropped from C, the vertex of the right angle, to the hypotenuse. Then

${\frac {1}{CD^{2}}}={\frac {1}{AC^{2}}}+{\frac {1}{BC^{2}}}.$

See also

• Pythagorean theorem