Answer
$x^3-5x^2+3x+9$
Work Step by Step
Let us consider that $a$ is a zero of a function with multiplicity $b$. Then this factor of the function can be expressed as: $(x-a)^b$.
We are given that the degree is $3$, and the zeros are −1 (multiplicity 1) and 3 (multiplicity 2).
Therefore, we can write the equation of the function as:
$f(x)=(x+1)(x+1)(x-3)^2 \\=x^3-5x^2+3x+9$
