Solution: Suppose the line segment joining the points P(1 , 2 3 ) and Q (-3 , 4 , -5 ) is divided by the xy - plane at a point R in the ratio . Then , the coordinates of R are
i.e.
Since R lies on xy-plane i.e. Z = 0 . Therefore , z-coordinate of R must be zero .
i.e.
So , the required ratio is or 3:5 .
Putting in (1) , we obtain the coordinates of R as