Chapter 9 - Section 9.4 - Imaginary Numbers as Solutions of Quadratic Equations - Exercise Set - Page 655: 13

$10+i\sqrt{3}$

Using the properties of radicals and that $i=\sqrt{-1}$, then the given expression, $ 10+\sqrt{-3} ,$ is equivalent to \begin{array}{l}\require{cancel} 10+\sqrt{-1}\cdot\sqrt{3} \\\\= 10+i\cdot\sqrt{3} \\\\= 10+i\sqrt{3} .\end{array}