If x2 is \(x^2\) then use the quadratic formula.
\(x^2+9x+16=0\)
\(x = {-9 \pm \sqrt{9^2-4 \cdot 1 \cdot 16} \over 2 \cdot 1}\)
\(x = {-9 \pm \sqrt{81-64} \over 2}\)
\(x = {-9 \pm \sqrt{17} \over 2}\)
Since this is irrational, the expression cannot be factored.
