## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$b=\pm 18$
$x^{2}+bx+81$ By following the perfect-square trinomial rule $(A+B)^{2}=A^{2}+2AB+B^{2}$, we see that $A^{2}=x^{2}$ and $B^{2}=81$. The square roots of $A^{2}$ and $B^{2}$ are $\pm x$ and $\pm 9$. Because of the perfect-square trinomial rule, $bx=2\cdot x\cdot B \qquad$..substitute $9$ for $B$ and divide the expression with $x$. $b=2\cdot\pm 9$ $b=\pm 18$