Answer
$\sqrt {a^2+b^2}$ units
Work Step by Step
To calculate the distance $d$ between two points, we have:
$d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}$
Substitute the $x$ and $y$-coordinates of the given points to obtain:
$d=\sqrt{(0-a)^2+(0-b)^2}=\sqrt{(-a)^2+(-b)^2}=\sqrt {a^2+b^2}$
