We have a 3,4,5 right triangle.
I understand everything posted above; however, I don't understanding anything below. Everything here is understood now.
A,B,C,D are constants to be determined, and set 2.2.9
Then, from and 2.2.8, 2.2.9, we see that with the choice A = 3, C = 4, Equation 2.2.2 becomes