Answer:
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
