Question

Help Plz!

Answer 1

Are you familiar with polynomial long division or polynomial synthetic division?

Answer 2

Yeah a little

Answer 3

Because 3 is a zero (aka root or solution), you know that x = 3.
x = 3
x - 3 = 3 - 3
x - 3 = 0
(x - 3) is the factor for x = 3. We know that factor * another factor = product. (product is polynomial here) If factor * another factor = product, then product / factor = another factor. This means we can divide the polynomial by the factor we just found.

x^3 -4x^2 -3x +18 = 0
We'll use synthetic division. We divide by the zero itself (not the factor) to get the same effect as dividing by the factor.