Prove (correctly) that if 1 = -1, then 2=1

This may not be entirely satisfied proof but you should get the idea.

Proof: Start with 1 = -1.

Then we know that if a= b then a + c = b + c and also a / c = b / c.

So we can add 1 to both sides.

We have 1 + 1 = -1 + 1   ⇒   2 = 0.

Now divide both sides by 2 and we would have 1 = 0.

Now add both sides by 1. This yields 2 = 1.

Therefore if 1 = -1 then 2 = 1.

QED