## College Algebra (10th Edition)

$\sqrt{(-9)\cdot(-9)}$ does not equal $\sqrt{(-9)}\cdot\sqrt{(-9)}$
$\sqrt{(-9)}\cdot\sqrt{(-9)} =3i\cdot 3i=9i^{2}=9(-1)=-9$, while $\sqrt{(-9)\cdot(-9)}=\sqrt{81}=+9$