robinbloke | Found it!

I used to know this proof, but forgot it (as I do most things) but due to the wonders of the internet, I've found it again.

step 1: a = b

step 2: a² = ab [ after you multiply both sides by a ]

step 3: a² - b² = a² - b² [ subtract b² from both sides ]

step 4: (a + b)(a - b) = b(a - b) [ factor both sides ]

step 5: (a + b) = 1b [ after you divide both sides by (a - b) ]

step 6: 2b = 1b [ since a = b, (a + b) = 2b ]

step 7: 2 = 1 [ after you divide both sides by b ]

For a pint, anyone know which step is wrong, and why?

(Now corrected so that the squares look correct!)