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Please Solve RD Sharma Class 12 Chapter 28 The Plane Exercise 28.11 Question 24 Maths Textbook Solution.

Answers (1)

Answer:  -2

Hint: Use formula  \frac{x-x_{1}}{a_{1}}=\frac{y-y_{1}}{b_{1}}=\frac{z-z_{1}}{c_{1}}

Given:  \frac{x-2}{6}=\frac{y-1}{\lambda}=\frac{z+5}{-4} \text { and } 3 x-y-2 z=7

Solution: Here given midline

            \frac{x-2}{6}=\frac{y-1}{\lambda}=\frac{z+5}{4}  is perpendicular to plane  3 x-y-2 z=7

We know that line

            \frac{x-x_{1}}{a_{1}}=\frac{y-y_{1}}{b_{1}}=\frac{z-z_{1}}{c_{1}}  is perpendicular to plane  a_{2} x+b_{2} y+c_{2} z+d_{2}=0  if

            \frac{a_{1}}{a_{2}}+\frac{b_{1}}{b_{2}}+\frac{c_{1}}{c_{2}}=0

So, normal vector of plane is parallel to line.

So, direction ratios of normal to plane are proportional to the direction of line.

            Here,  \frac{6}{3}=\frac{\lambda}{-1}=\frac{-4}{-2}

By cross multiplying the last two we have

            -2 \lambda=4 \Rightarrow \lambda=-2

 

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