Righttrianglealtitudetheorem means that in a right triangle, the height on the hypotenuse is the median term of the ratio of the projection of two right-angled sides on the hypotenuse, and the right-angled side is the median term of the ratio of the projection of this right-angled side on the hypotenuse to the hypotenuse.

The projection theorem of right triangle, also known as Euclid theorem, is that in a right triangle, the height on the hypotenuse is the proportional average of the projections of two right angles on the hypotenuse, and each right angle is the proportional average of the projection of this right angle on the hypotenuse and the hypotenuse.

1822, French mathematician Poncelet published the first systematic work on projective geometry. He was the first mathematician to realize that projective geometry is a new branch of mathematics.

Projective geometry is widely used in aviation, surveying, drawing and photography.