Pythagoras, Pythagorean, Euclidean, Gravitational Lensing, Symmetry.
A’ = (b-a)². The area of the big square A must be the sum of the small square A’ plus 4 times the area of one triangle (equation 2, Figure 3). Using this equality and some algebra, the desired result is obtained: Figure 3: Steps to obtain the Pythagorean equation under the conditions of Figure 1.