Answer
$d(P_1, P_2)=|a|\sqrt2$
Work Step by Step
The distance between the points $P_1=(x_1, y_1)$ and $P_2=(x_2, y_2)$, is given by the formula:
$d(P_1, P_2)=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}$
If we plug in the coordinates of the two given points given into the formula above, we'd have:
$d(P_1, P_2)=\sqrt{(0-a)^2+(0-a)^2}=\sqrt{a^2+a^2}=\sqrt{2a^2}=|a|\sqrt2$
