Generating function on Lehman's Mathematics for Computer Science

Question

I am reading Lehman's Mathematics for Computer Science. In chapter 16 Generating Functions.enter image description here I couldn't see how $1-x-x^2 = (x-r_1)(x-r_2)$. Shouldn't it be $1-x-x^2 = -1(x-r_1)(x-r_2)$? Since $r_1 r_2 = r_1+r_2 = -1$, $1-x-x^2 = -1(x-r_1)(x-r_2) = (1-x/r_1)(1-x/r_2)$?

Answer 1

Yes, you're right. This is a typo. It should be $-(x-r_1)(x-r_2)$.