There exists a pair of similar, but not congruent, triangles.

"You remember what are the properties of two similar triangles?"

For any similar triangle the ratio of the length of the sides remains the same.

Note that since this ratio is independent of time, one can take arbitrary times and achieve similar triangles.

In this figure we see two similar triangles, both having parts of the projection line (green) as their hypotenuses.

It was a simple matter of similar triangles, easy to see with a diagram but hard to keep straight in the head.

The angle where meets is common to two similar triangles with bases and respectively.

The height is calculated using the principle of similar triangles.

Like a triangle with a similar smaller triangle set on each side.

Multiplication was done by mechanisms based on the geometry of similar right triangles.