Quote:
Originally Posted by joepole
Actually, step 3 is fine, the distributive property was used correctly.
The problem is that between 3 and 4 you divide both sides by (a + b  c) which, according to the initial equation, is 0. You can't divide by 0.

Yes, the distributive property was used correctly, but it shouldn't have been used at all. Combining like terms is a fundamental of algebra and the author avoided it entirely in order to get the outcome that he did.
Go to
http://www.algebrahelp.com/calculators/equation/ and run the equation from step 2 and you'll see what I mean.
Improper calculation = invalid outcome!