#### Answer

Answer:
$x^{2}$ + 18x + 81

#### Work Step by Step

$(x + 9 )^{2}$
This will result in a perfect square trinomial, which can be generalized as $(a + b )^{2}$ = $a^{2}$ + 2ab + $b^{2}$.
Here, a = x, and b = 9.
Thus,
$(x + 9 )^{2}$ = $x^{2}$ + 2(9)(x) + $9^{2}$ = $x^{2}$ + 18x + 81.