Why does multiplying two negative numbers equal a positive number?
In: 1210
We want to show -a * – b = a * b, where a and b are real numbers.
-a * – b
= -1 * a * -1 * b
= -1 * -1 * a * b
So what we need is to show that -1 * -1 = 1.
Well 1 – 1 = 0
And -1 * (1 – 1) = -1 * 0 = 0
Which means -1 * 1 + -1 * -1 = 0
Thus -1 + – 1 * -1 = 0
Which means -1 * -1 must be equal to 1.
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