Answer
$\sqrt{21}$
Work Step by Step
The distance $d$ from $P_1(x_1,y_1,z_1)$ to $P_2(x_2,y_2,z_2)$ is
$d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2+(z_2-z_1)^2}$.
Hence, here
$d=\sqrt{(4-0)^2+(1-0)^2+(2-0)^2}\\
d=\sqrt{4^2+1^2+2^2}\\
d=\sqrt{16+1+4}\\
d=\sqrt{21}$.
