Question 246656
First factor the common factor:
f(x)=x^3+x^2 -20x
f(x)=x(x^2+x-20)


Now, factor the trinomial:
f(x)=x(x+5)(x-4)


Set each factor equal to 0.
x=0, x=-5, and x=4


You might even want to check this with a graphing calculator:
{{{graph(300,300,-6,6,-60,60, x^3+x^2-20x)}}}


Dr. Robert J. Rapalje, Retired
Seminole State College of Florida
Altamonte Springs Campus