Two lines L 1  :  x = 5 , y 3 - α = z - 2 and L 2  :  x = α , y - 1 = z 2 -…
Two lines and are coplanar. Then can take value(s)
- 1
- 2
- 3
- 4
Solution
$\frac{x-5}{0} = \frac{-y}{\alpha-3} = \frac{z}{-2}$
$\frac{x-\alpha}{0} = \frac{y}{-1}= \frac{z}{2-\alpha}$
$\begin{vmatrix} 5-\alpha & 0 & 0 \\ 0 & 3-\alpha & -2 \\ 0 & -1 & 2-\alpha \end{vmatrix} = 0$
$(5-\alpha) \cdot ((3-\alpha) \cdot (2-\alpha) - 2) = 0$
$(\alpha - 5) \cdot (\alpha^2 - 5\alpha + 6 - 2) = 0$
$(\alpha - 5) \cdot (\alpha^2 - 5\alpha + 4) = 0$
$\alpha = 1, 4, 5$
Asked in: JEE Advanced 2013 (Paper 2)
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