consider two circles of radius r1 and r2, centres (x1, y1) and (x2, y2). there are two lines that are tangents to BOTH these circles that DON' T cross the line joining the centres of the circles (clearly there are two more that do cross the line joining the centres of the circles). Anyone know how to calculate the position of the points at which the tangents touch the circles (that is, all four points)

thanks,