Another one = two

Assume a = b


multiply both sides by a...


a squared = ab


subtract b squared from both sides...


(a squared – b squared) = ab – b squared


factorize...


(a + b)(a – b) = b(a – b)


divide both sides by (a – b)...


(a + b) = b


Let a = b = 1


2 = 1 QED

a - b = 0. You are dividing by zero.

I liked the calculus one a lot better. This one is very trite. I first heard it when I was about 13, and proudly went to tell my Grandpa that I had a great mathematical paradox. Before I even started it, he said "Oh I expect it's dividing by zero", and I went away disappointed.


He didn't say it in a mean way, just as an observation, and he was a Nobel prize winner so I expect quite a lot of things seemed obvious to him!


Oh no!! Not again!

what does QED mean?

"that we sought is thus demonstrated"


Or something to that effect. It means the proof is complete.


A guy I knew who took both math and latin I think translated it best: "Whoop there it is"