When you multiply a negative number twice, why you get a positive number? I'll explain it to you in an easy way. -1+1=0. It means that if you multiply any number x by A number that is the product of -1 and x, you get 0. To generalize, if any number is x, x+(-1)*x=0. Now define x as -1. (x = -1) x=-1, and the equation is x+(-1)*x=0. To add a number to -1 and get 0, you need to add 1. x+(-1)*x=0 can be expressed as -1+(-1)*(-1)=0. If you add any number to -1 to get 0, that number is 1. Since x=-1 before, this equation becomes (-1)*(-1)=(-1)*x=1. -> (-1)*(-1)=1 So you learn that if you multiply a negative by a negative, you get a positive.