Factorize $3x^3 + 2x + 5$:

Substituting $x=-1$ gives $-3 - 2 + 5 = 0$, so $(x+1)$ is a factor. Dividing $3x^3 + 2x + 5$ by $(x+1)$ leaves the quadratic $3x^2 - 3x + 5$.