The points P = (x1, y1) and ! = (x2, y2) are the intersections of the parabola y^2 = 4ax, where a > 0, and a line passing through the focus of the parabola. Then the distance PQ can be expressed in the form c1x1 + c2x2 + c3a, where c1, c2, and c3 are constans. Compute c1 + c2 + c3.
