Q120 / 225 · JEE Main 2005 · Mathematics

If the angle $\theta$ between the line $\frac{x+1}{1}=\frac{y-1}{2}=\frac{z-2}{2}$ and the plane $2 x-y+\sqrt{\lambda} z+4=$ 0 is such that $\sin \theta=\frac{1}{3}$ the value of $\lambda$ is

  • Correct answer
    A
    $\frac{5}{3}$
  • B
    $\frac{-3}{5}$
  • C
    $\frac{3}{4}$
  • D
    $\frac{-4}{3}$

Solution

Angle between line and normal to plane is $\cos \left(\frac{\pi}{2}-\theta\right)=\frac{2-2+2 \sqrt{\lambda}}{3 \times \sqrt{5+\lambda}}$ where $\theta$ is angle between line \& plane $$ \Rightarrow \sin \theta=\frac{2 \sqrt{\lambda}}{3 \sqrt{5+\lambda}}=\frac{1}{3} $$ $\Rightarrow \lambda=\frac{5}{3}$.

Hence, the correct answer is option: 'A'.

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