if $\displaystyle l:ax+by+c=0$ is a line in the 2-space and $\displaystyle P_0(x_0,y_0)$ is a point, then the distance between the point $\displaystyle P_0$ and the line $\displaystyle l$ is:

$\displaystyle \frac{|ax_0+by_0+c|}{\sqrt{a^2+b^2}}$

Can anyone explain briefly to me why is that so? Does it based on the concept of orthogonal projection?