# How do you solve x^2-18x+81=0 by factoring?

It is ${x}^{2} - 18 x + 81 = 0 \implies {x}^{2} - 2 \cdot 9 \cdot x + {9}^{2} = 0 \implies {\left(x - 9\right)}^{2} = 0 \implies x = 9$
We used the identity ${\left(a - b\right)}^{2} = {a}^{2} - 2 a b + {b}^{2}$