# How do you multiply the radicals 5sqrt2 * 8sqrt2?

$5 \sqrt{2} \cdot 8 \sqrt{2} = 5 \cdot 8 \cdot \sqrt{2} \cdot \sqrt{2} = 40 \cdot 2 = 80$
In case it is not clear $\sqrt{2} \cdot \sqrt{2} = 2$ because that's how square root is defined.
Alternatively: $\sqrt{2} \cdot \sqrt{2} = \sqrt{2 \cdot 2} = \sqrt{4} = 2$