[oblomov]

Sorry, since you divided by (a-b), this equality holds only if a <> b. So a and b both can't be 1.

[JeffAtlanta]

Sorry, since you divided by (a-b), this equality holds only if a <> b. So a and b both can't be 1.

I think he is aware of that. The proof in his post is a very famous one.

[antiRepublicrat]

You'd be amazed how many people can't figure that one out.