# How do you factor the expression r^2-4rs+4s^2?

${r}^{2} - 4 r s + 4 {s}^{2} = {\left(r - 2 s\right)}^{2}$
${r}^{2} - 4 r s + 4 {s}^{2}$
$\text{ }$
$= {r}^{2} - 2 \left(r\right) \left(2 s\right) + {\left(2 s\right)}^{2}$
$\text{ }$
$= {\left(r - 2 s\right)}^{2}$