Two lines L 1  :  x = 5 , y 3 - α = z - 2 and L 2  :  x = α , y - 1 = z 2 -…

Two lines  L 1  :  x = 5 , y 3 - α = z - 2  and  L 2  :  x = α , y - 1 = z 2 - α  are coplanar. Then α  can take value(s)
  1. 1
  2. 2
  3. 3
  4. 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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