(x+3) is not a factor of x³+x²-x+6
1) In this question, we can use The Factor Theorem that states:
2) So let's divide that given Polynominal by that binomial, if we have an exact division then (x+3) is a factor of that Polynomial.
Note that since this is not an exact division then we can conclude that
3) (x+3) is not a factor of x³+x²-x+6