(i) Let the point p(x,y) lies on the line joining the points A(1,2) and B(3,6).
`therefore "P,A and B are collinear."`
`rArr" "=1/2|{:(x,y,1),(1,2,1),(3,6,1):}|=0`
`rArr x(2-6)-y(1-3)+1(6-6)=0`
`rArr -4x+2y=0 rArr y=2x`
(ii) Let the point P(x,y) lies on the line joining the points A(3,1) and B(9,3).
`therefore" P,A and B are collinear".`
`rArr" "1/2|{:(x,y,1),(3,1,1),(9,3,1):}|=0`
`rArr x(1-3)-y(3-9)+1(9-9)=0`
`rArr" "-2x+6x=0=rArrx-3y=0`