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

$\left({r}^{2} - 1\right) \left({r}^{2} - 4\right)$
${r}^{4} - 5 {r}^{2} + 4 = \left({r}^{2} - 1\right) \left({r}^{2} - 4\right)$