Given points are A(3,4),B(x1,y1) and C(x2,y2) since, 3,x1,x2 and 4,y1,y2 are in AP. Then, ;;2x1=3+x2 and 2y1=4+y2⇒;;x1=;23+x2 and y1=;24+y2 This shows that B is the mid-point of the line segment joining A and C. Hence, A,B and C are collinear.