Chapter 8 - Section 8.5 - Quadratic Functions and Their Graphs - Exercise Set - Page 519: 64

$x=-7\pm\sqrt{29}$

Using the completing the square method, the solutions of the given quadratic equation, $ x^2+14x+20=0 ,$ is \begin{array}{l}\require{cancel} x^2+14x=-20 \\\\ x^2+14x+\left( \dfrac{14}{2} \right)^2=-20+\left( \dfrac{14}{2} \right)^2 \\\\ x^2+14x+49=-20+49 \\\\ (x+7)^2=29 \\\\ x+7=\pm\sqrt{29} \\\\ x=-7\pm\sqrt{29} .\end{array}