This is absolutely great, easy to follow and explain. I love it! However it is incomplete, and thus doesn’t work as a proof. As the angles increase, the 2 tria

This is absolutely great, easy to follow and explain. I love it! However it is incomplete, and thus doesn’t work as a proof. As the angles increase, the 2 triangles will no longer be inside the rectangle. Signs start to flip around and extra work is needed to show the sin(a+b) and cos(a+b) equations are sound. The bright side is this is a good asignment for the student.