It's an old chestnut. If A=2 then A-2=0, so the line where you divide both sides by A-2 is invalid since you can't divide by zero (as the answer is always infinity)
if A = 2 then (A-2) = 0
from line 5 to 6 both sides of equation are divided by (A-2) or 0
you cannot divide by zero
hence error in the argument trying to prove 2 = 1