If we perform sintetic division on the polynomiapl P(x), assuming that x = -2 is a root, then we have:
notice that the last number on the final row is 0, this means that by the factor theorem, since the residue is 0, we have that (x+2) is a factor of the polynomial P(x). Also, we can evaluate -2 on P(x) to get:
so, P(-2) = 0