# How do you factor 25b^2 -60b +36?

$25 {b}^{2} - 60 b + 36$ is of the form ${A}^{2} - 2 A B + {B}^{2}$ where $A = 5 b$ and $B = 6$.
$25 {b}^{2} - 60 b + 36 = {\left(5 b\right)}^{2} - \left(2 \times 5 b \times 6\right) + {6}^{2}$
$= {\left(5 b - 6\right)}^{2}$