# Chapter 9 - Section 9.4 - Imaginary Numbers as Solutions of Quadratic Equations - Exercise Set: 12

$9+2i$

#### Work Step by Step

Using the properties of radicals and that $i=\sqrt{-1}$, then the given expression, $9+\sqrt{-4} ,$ is equivalent to \begin{array}{l}\require{cancel} 9+\sqrt{-1}\cdot\sqrt{4} \\\\= 9+i\cdot\sqrt{(2)^2} \\\\= 9+i\cdot2 \\\\= 9+2i .\end{array}

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