Length of 3D Vector - Square root rules

Question

I have a 3D vector $r(u)=(16u^3,0,16)$, which I want to find the length of. I do this by $|r(u)|=\sqrt{(16u^3)^2+16^2}$

Could someone explain how $\sqrt{(16u^3)^2+16^2}$ yields $16 \sqrt{u^6+1}$?

Thanks

Answer 1

Hint:

$$\sqrt{ab}=\sqrt{a}\sqrt{b}$$

when $a,b\in\mathbb{R}_{\geq 0}$.