Question

(Sorry for the spam, making sure these are right) One zero of the polynomial function f(x)=x^3-9x^2+20x is x=0. What are the polynomial function? Choices:

Answer 1

Replace f(x) with 0 and solve for x. We do this because the x intercepts always occur when y = 0. Keep in mind that y = f(x).

f(x)=x^3-9x^2+20x

0=x^3-9x^2+20x

x^3-9x^2+20x = 0

x(x^2-9x+20) = 0 .... factor out GCF x

x(x-5)(x-4) = 0 ... factor the stuff inside

x = 0 or x-5 = 0 or x-4 = 0 ... zero product property

x = 0 or x = 5 or x = 4

The roots or zeros are 0, 5, 4

Answer: Choice D