# Whats the square root of negative 8 times the square root of negative 10?

Sep 22, 2015

This is written as:

$\sqrt{- 8} \sqrt{- 10}$

What you can do is factor out the two $\sqrt{- 1}$ and multiply them, canceling the square root, but not changing the sign of the number under it:

$\sqrt{- 8} \sqrt{- 10} = \sqrt{- 1} \cdot \sqrt{8} \cdot \sqrt{- 1} \cdot \sqrt{10}$

$= - \sqrt{80}$

$= - \sqrt{16 \cdot 5}$

$= \textcolor{b l u e}{- 4 \sqrt{5}}$