# How do you use the factor theorem to determine whether x-1 is a factor of f(x)=x^3+4x-5?

Calculate $f \left(1\right)$.
If $f \left(1\right) = 0$, then $x - 1$ is a factor of $f$. So let's calculate $f \left(1\right)$.
$f \left(1\right) = 1 + 4 - 5 = 5 - 5 = 0$. So $1$ is a root of this polynomial, and $x - 1$ is a factor of it.