Sheet # 61/Integer/Why -1 x - 1 = 1?

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There is no concrete example of multiplying negative numbers, but here is a proof for it.

First start with the sum of opposites:

- 3 + 3 = 0

Now multiply both sides of the equation by a negative number:
- 4(- 3 + 3) = 0 * - 4

This gives
(- 4* - 3) +( - 4 * 3) = 0

We know that 3 groups of negative four is negative twelve:
(- 4 * - 3 )+ ( -12 ) = 0

So what number plus negative twelve will give me zero? positive twelve. Therefore, - 4 * -3 = 12