What is Factor theorem?

Factor Theorem:

The factor theorem states that if p(x) is a polynomial of degree n greater than or equal to 1 and ‘a’ is any real number, then x-a is a factor of p(x), if p(a)$=$0.

For example,

$x + 1$ is a factor of $P(x) = -3x^2 – x + 2$ if and only if $P(-1) = 0$.

$P(-1) =  -3(-1)^2 – (-1) + 2 = -3+1+2 = 3-3 = 0$.