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Provide Solution for RD Sharma Class 12 Chapter 27 Straight Line in Space Exercise Very Short Answer Question 21

Answers (1)

Answer:

Required angle is  \frac{\pi}{2}

Hint:

Use equation of a line in space.

Given:

 2 x=3 y=-z \text { and } 6 x=-y=-4 z

Solution:

The equation of the given lines can be rewritten as,

\frac{x}{3}=\frac{y}{2}=\frac{z}{-6} \text { and } \frac{x}{2}=\frac{y}{-12}=\frac{z}{-3}

We know that angle between the lines

\frac{x-x_{1}}{a_{1}}=\frac{y-y_{1}}{b_{1}}=\frac{z-z_{1}}{c_{1}} \text { and } \frac{x-x_{2}}{a_{2}}=\frac{y-y_{2}}{b_{2}}=\frac{z-z_{2}}{c_{2}}    is given by,

\cos \theta=a_{1} a_{2}+b_{1} b_{2}+c_{1} c_{2}

Let,

\theta=\frac{a_{1} a_{2}+b_{1} b_{2}+c_{1} c_{2}}{\sqrt{a_{1}^{2}+b_{1}^{2}+c_{1}^{2}} \sqrt{a_{2}^{2}+b_{2}^{2}+c_{2}^{2}}}

Let  \theta  be the angle between the given lines

\begin{aligned} &\cos \theta=\frac{3 \times 2+2 \times(-12)+(-6) \times(-3)}{\sqrt{3^{2}+2^{2}+(-6)^{2}} \sqrt{2^{2}+(-12)^{2}+(-3)^{2}}} \\ & \end{aligned}

=\frac{6-24+18}{\sqrt{49} \sqrt{157}}

\begin{aligned} &=0 \\ & \end{aligned}

\theta=\frac{\pi}{2}

Thus, the angle between the given lines is  \frac{\pi}{2}

 

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