# How do you multiply sqrt81*sqrt36?

Jul 3, 2018

$\pm 54$

#### Explanation:

Given: $\sqrt{81} \cdot \sqrt{36}$

Use the fact that $\sqrt{a} \cdot \sqrt{b} = \sqrt{a b} \setminus \forall a , b \ge 0$.

$= \sqrt{81 \cdot 36}$

$= \sqrt{2916}$

$= \sqrt{{54}^{2}}$

Now, use the fact that $\sqrt{{a}^{2}} = \pm a$.

$= \pm 54$

Jul 3, 2018

$\sqrt{81} \cdot \sqrt{36} = \pm 54$

#### Explanation:

It can be done either of 2 ways: take square root first, then multiply
or multiply first, then take square root.

$\sqrt{81} \cdot \sqrt{36} = \pm 9 \cdot \pm 6 = \pm 54$

$\sqrt{81} \cdot \sqrt{36} = \sqrt{81 \cdot 36} = \sqrt{2916} = \pm 54$

I hope this helps,
Steve