Question
The ratio in which the join of points $$\left( {1,\, - 2,\,3} \right)$$ and $$\left( {4,\,2,\, - 1} \right)$$ is divided by $$XOY$$ plane is :
A.
$$1:3$$
B.
$$3:1$$
C.
$$ - 1:3$$
D.
None of these
Answer :
$$3:1$$
Solution :
Let $$A\left( {1,\, - 2,\,3} \right)$$ and $$B\left( {4,\,2,\, - 1} \right)$$
Let the plane $$XOY$$ meet the line $$AB$$ in the point $$C$$ such that $$C$$ divides $$AB$$ in the ratio $$k : 1,$$ then
$$C \equiv \left( {\frac{{4k + 1}}{{k + 1}},\,\frac{{2k - 2}}{{k + 1}},\,\frac{{ - k + 3}}{{k + 1}}} \right)$$
Since $$C$$ lies on the plane $$XOY$$ i.e., the plane $$z = 0,$$ therefore
$$\frac{{ - k + 3}}{{k + 1}} = 0 \Rightarrow k = 3$$