-1 because the exponent is not distributed to the negative sign, so -1^2=-1*1^2=-1
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"If we can agree that a negative number is just a positive number multiplied by -1, then we can always write the product of two different negative numbers this way:
(-a)(-b) = (-1)(a)(-1)(b) = (-1)(-1)ab
or example,
-2 * -3 = (-1)(2)(-1)(3)
= (-1)(-1)(2)(3)
= (-1)(-1) * 6
So then the real question is,
(-1)(-1) = ?
and the answer is that the following convention has been adopted:
(-1)(-1) = +1
This convention has been adopted for the simple reason that any other convention would cause something to break.
For example, if we adopted the convention that (-1)(-1) = -1, the distributive property of multiplication wouldn't work for negative numbers:
[(a)(1+a) = a(1) + (a)(a)] where a = -1
(-1)(1 + -1) = (-1)(1) + (-1)(-1)
(-1)(0) = -1 + -1
0 = -2
As Sherlock Holmes observed, "When you have excluded the impossible, whatever remains, however improbable, must be the truth."
Since everything except +1 can be excluded as impossible, it follows that, however improbable it seems, (-1)(-1) = +1. "
source: mathforum.org/dr.math/faq/faq.negxneg.html