Pythagoras, Pythagorean, Euclidean, Gravitational Lensing, Symmetry.
clear from the last box that: Due to the same reasons as the former case, all the angles between the blue line or any red line are 90 degrees. Because the green line dissects the right angle, α + β = 90°. The conclusion from the two former points: the triangle formed by the red, blue, and green