Look at the right triangle ABC A student made the following chart to prove that AB^2 + BC^2 = AC^2. (Look at attached images)
What is the flaw in the student’s proof?

Let x have probability generating function gx (s) and let un generating function u(s) of the sequence uo, u1, satisfies p(x > n). show that the (1- s)u(s) = 1 - gx(s), whenever the series defining these generating functions converge.