Answer
$(x-9)^2$.
Work Step by Step
The given polynomial is
$=x^2-18x+81$
Write the the polynomial as $a^2-2ab+b^2$.
$=x^2-2(x)(9)+9^2$
Use perfect square trinomial pattern
$a^2-2ab+b^2=(a-b)^2$
We have $a=x$ and $b=9$.
$=(x-9)^2$
Hence, the factor of the given polynomial is $(x-9)^2$.
