Answer
(x-3+y)(x-3-y)
Work Step by Step
$x^{2}$-18x+81-$y^{2}$=($x^{2}$-2*x*9+$9^{2}$)-$y^{2}$=
$(x-3)^{2}$-$y^{2}$=(x-3+y)(x-3-y)
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