# How do you find the missing number or term to make a perfect square trinomial. x^2 - 18x +___ ?

$81$
If you use $81$ you get:
${x}^{2} - 18 x + 81 = {\left(x - 9\right)}^{2}$
It has to be a number that multiplied by $2$ gives $18$; this is $9$ that has to appear squared in your missing place.