Answer
$(3a-1)\sqrt{a}$
Work Step by Step
Factor each radicand so that one of the factors is a perfect square to obtain:
$=\sqrt{9a^2(a)} -\sqrt{a}
\\=\sqrt{(3a)^2(a)}-\sqrt{a}$
Simplify each radical to obtain:
$=3a\sqrt{a} - \sqrt{a}$
Combine like radicals to obtain:
$=(3a-1)\sqrt{a}$
