Question
If the lines $\frac{\text{x}-1}{-3}=\frac{\text{y}-2}{2\text{k}}=\frac{\text{z}-3}{2}\ \text{and}\ \frac{\text{x}-1}{3\text{k}}=\frac{\text{y}-1}{1}=\frac{\text{z}-6}{-5}$ are perpendicular, find the value of k.

Answer

The given lines are
$\frac{\text{x}-1}{-3}=\frac{\text{y}-2}{2\text{k}}=\frac{\text{z}-3}{3}$
and $\frac{\text{x}-1}{3\text{k}}=\frac{\text{y}-1}{1}=\frac{\text{z}-6}{-5}$
Direction ratios of two lines are -3, 2k, 2 and 3k, 1, -5
Since the lines are perpendicular
$\therefore$ (-3)(3k) + (2k)(1) + (2)(-5) = 0
$\therefore$ -9k + 2k - 10 = 0
⇒ -7k = 10
$\therefore\ \text{k}=-\frac{10}{7}$

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