# Is 81 + 18y + y^2 a perfect square trinomial and how do you factor it?

${a}^{2} + 2 a b + {b}^{2} = {\left(a + b\right)}^{2}$
with $a = 9$ and $b = y$
$81 + 18 y + {y}^{2} = {9}^{2} + 2 \cdot 9 y + {y}^{2} = {\left(9 + y\right)}^{2}$