If the point x1+tx2−x1,y1+ty2−y1 divides the join of x1,y1 and x2,y2 internally, then
t<0
0<t<1
t>1
t=1
x coordinate of the point x1+tx2−x1,y1+ty2−y1 can be rewrite as
x1+tx2-tx11=x11-t+tx2t+1-t
this gives the x -coordiante of a point which divides the line segment joining the given points in the ratio t:1-t internally
here 1-t>0
⇒t<1