If the point [x1+s(x2−x1),y1+s(y2−y1)] divides the join of (x1,y1) and(x2,y2) internally, then

P(x1+s(x2−x1)),y1+s(y2−y1) P=[(1−s)x1+sx21−s+s,(1−s)y,+sy21−s+s]  P divides A(x1,y1)&B(x2,y2) in the ratio s : 1−s internally⇒s1−s>0⇒s(s−1)>0 ⇒(s−0)(s−1)<0 ⇒0