Question
Given the line $$L:\frac{{x - 1}}{3} = \frac{{y + 1}}{2} = \frac{{z - 3}}{{ - 1}}$$ and the plane $$\pi \,:x - 2y = z.$$ Of the following assertions, the only one that is always true is :
A.
$$L$$ is $$ \bot $$ to $$\pi $$
B.
$$L$$ lies in $$\pi $$
C.
$$L$$ is parallel to $$\pi $$
D.
None of these
Answer :
$$L$$ lies in $$\pi $$
Solution :
Since $$3\left( 1 \right) + 2\left( { - 2} \right) + \left( { - 1} \right)\left( { - 1} \right) = 3 - 4 + 1 = 0$$
$$\therefore $$ given line is $$ \bot $$ to the normal to the plane i.e., given line is parallel to the given plane.
Also $$\left( {1,\, - 1,\,3} \right)$$ lies on the plane $$x - 2y - z = 0$$ if $$1 - 2\left( { - 1} \right) - 3 = 0$$ i.e. $$1 + 2 - 3 = 0$$ which is true.
$$\therefore \,L$$ lies in plane $$\pi .$$