# Chapter 5 - Polynomials and Factoring - 5.7 Solving Quadratic Equations by Factoring - 5.7 Exercise Set - Page 351: 23

$x=\left\{ -7,3 \right\}$

#### Work Step by Step

Factoring the given equation, $x^2+4x-21=0 ,$ results to \begin{array}{l}\require{cancel} (x+7)(x-3)=0 .\end{array} Equating each factor to zero (Zero Product Principle), then the solutions to the equation, $(x+7)(x-3)=0 ,$ is \begin{array}{l}\require{cancel} x+7=0 \\\\ x=-7 ,\\\\\text{OR}\\\\ x-3=0 \\\\ x=3 .\end{array} Hence, $x=\left\{ -7,3 \right\} .$

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