Which equation shows an example of the associative property of addition?
1) -7i + 7i = -7(i + 7i)
2) -7i + 7i = 7i(-7i + i)
3) 7i - (-7i + i) = (7i - 7i) + (7i - i)
4) (7i - i)(7i - i) = -7i(i)
5) Cannot be determined