# Possible fake proof of $1= -1$ [duplicate]

Possible Duplicate:
-1 is not 1, so where is the mistake?
Simple Complex Number Problem: 1 = -1

Well, I remembered this after having Algebra II a year ago, is it possible that this is a valid proof that $1 = -1$?

$$1 = \sqrt{1} = \sqrt{-1\cdot-1} = \sqrt{-1} \cdot \sqrt{-1} = i \cdot i = i^2 = -1$$

$$\therefore 1 = -1$$

So is this actually fully valid? Or can it be disproved?

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## marked as duplicate by MJD, Argon, Douglas S. Stones, Brian M. Scott, Gerry MyersonSep 9 '12 at 0:41

– Envious Page Sep 9 '12 at 0:34
Actually this one is more like Simple Complex Number Problem: 1 = -1 – MJD Sep 9 '12 at 0:39
Do you really think it is even remotely possible that there is a valid proof - and a proof using nothing more than two lines of high school algebra, at that - a valid proof that $1=-1$? – Gerry Myerson Sep 9 '12 at 0:41
Duplicate: Square root of 1 is (not) -1 – Argon Sep 9 '12 at 0:41
– Argon Sep 9 '12 at 0:42

I think the problem is between $\sqrt{ -1 \dot{} -1 }$ and $\sqrt{-1} \dot{} \sqrt{-1}$.

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