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 answerA$\frac{5}{3}$
- 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'.