When you multiply numbers, two negative signs cancel each other out. Therefore if four of the numbers are negative the product is positive. If either one or three numbers are negative, the product is negative.
1.a negative, b positive, c positive, d positive
2.a positive, b negative, c positive, d positive
3.a positive, b positive, c negative, d positive
4.a positive, b positive, c positive, d negative
5.a positive, b negative, c negative, d negative
6.a negative, b positive, c negative, d negative
7.a negative, b negative, c positive, d negative
8.a negative, b negative, c negative, d positive
