If the lines $\frac{1-x}{3} = \frac{3y-6}{k} - \frac{3-z}{-2}$ and $\frac{1-x}{2k}=\frac{y-5}{3}=\frac{6-z}{5}$ are perpendicular to each other, then $k$ is equal to
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → $\frac{10}{7}$
Given lines:
$\frac{1-x}{3}=\frac{3y-6}{k}=\frac{3-z}{-2}$
$\frac{1-x}{2k}=\frac{y-5}{3}=\frac{6-z}{5}$
Convert to symmetric form.
Line $L_{1}$ direction ratios:
$\frac{x-1}{-3}=\frac{y-2}{\frac{k}{3}}=\frac{z-3}{2}$
So DRs of $L_{1}$ are $(-3,\frac{k}{3},2)$.
Line $L_{2}$ direction ratios:
$\frac{x-1}{-2k}=\frac{y-5}{3}=\frac{z-6}{-5}$
So DRs of $L_{2}$ are $(-2k,3,-5)$.
Since lines are perpendicular, dot product of DRs is zero.
$(-3)(-2k)+\frac{k}{3}\cdot 3 + 2(-5)=0$
$6k + k - 10 = 0$
$7k = 10$
$k = \frac{10}{7}$
Final answer: $k=\frac{10}{7}$