SAT Mathematics Practice Test 7

Each of the options is a quadratic expression in vertex form. To rewrite the given expression in this form, the number 9 needs to be added to t he first two terms, because ${\mathit{x}}^2+6\mathit{x}+9$ is equivalent to ${\left(\mathit{x}+3\right)}^2$. Rewriting the number 4 as 9 – 5 in t he given expression yields ${\mathit{x}}^2+6\mathit{x}+9\mathit{–}5$, which is equivalent to ${\left(\mathit{x}+3\right)}^2\mathit{–}5$.