# How do you factor x^2 + 5x + 4?

Notice that $5 = 1 + 4$ and $4 = 1 \cdot 4$, so this can be factored as follows:
${x}^{2} + 5 x + 4 = \left(x + 1\right) \left(x + 4\right)$
$\left(x + a\right) \left(x + b\right) = {x}^{2} + \left(a + b\right) x + a b$