Answers

2015-06-27T12:22:50+08:00
(-a)(-b)=ab (positive=(negative)(negative))
(a)(b)=ab(positive =(positive)(positive))
(-a)(b)=-ab(negative=(positive)(negative) or vice versa)

generalization: like terms=positive
unlike terms=negative

rule. even no. of negative is equal to positive
. odd no. of negative is equal to negative
0