Proof that 2=1
Proof
1) . Given.
2) . Multiply both sides by a.
3) . Subtract from both sides.
4) . Factor both sides.
5) . Divide both sides by
6) . Substitute for .
7) . Addition.
8) . Divide both sides by .
Error
The quantity of is as , since one cannot divide by zero, the proof is incorrect from that point on.
Usually, if a proof proves a statement that is clearly false, the proof has probably divided by zero in some way.