We have seen in the illustrative model that the sine value ([math]\frac{a}{c}[/math]) of a right triangle (green) depends only on the value of angle [math]\alpha[/math]. Why is that so?[br]This result can be proven using Thales Theorem: just remember what Thales Theorem states.[br]In the following dynamic model, you can move orange points (slope-point, A, B and C).[br]You can use the "control box" to superimpose the green triangle you have been using until now on top of the geometrical structure (Thales Theorem).