# How do you factor y^2-5y+4?

Notice $1 + 4 = 5$ and $1 \times 4 = 4$
$\left(y - 1\right) \left(y - 4\right) = {y}^{2} - \left(1 + 4\right) y + \left(1 \times 4\right) = {y}^{2} - 5 y + 4$