math154 wrote:

LHowever, that is tedious, so we reverse the process and start with the remainder. By the Remainder Theorem, we have $r = ( - 3)^{20} = 3^{20}$ .
In the process of synthetic division, we have to multiply the constant term (after division) by $- 3$ , and then add it to the constant term of $x^20$ , which is $0$ , to that. Thus, our constant term (after division) is $\frac {3^{20}}{ - 3} = - 3^{19}$ .

I don't understand this part of the solution. Could you please be a little bit more specific? Thanks!