Answer
$f(x)=x^3-3x^2-x+3$
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 $-1$, $1$ and $3$.
Therefore, we can write the equation of the function as:
$f(x)=a(x+1)(x-1)(x-3)\\=a(x^3-3x^2-x+3)$
When $a=1$, the function can be written as:
$f(x)=x^3-3x^2-x+3$
