I've asked several of my friends about this question, but nobody knows where to start with it, and unfortunately, neither do I. Here it is:

Given point A(x1,y1) and the line ax+by+c=0, show the distance from Point A to the line is d=[|ax1+by1+c|/root(a^2 + b^2)]. Note that ax+by+c=0 corresponds to a vertical line if b=0 and to a horizontal line if a=0.

Any help would be appreciated. Thank you