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Explain Solution R.D.Sharma Class 12 Chapter 27 Straight Line in Space Exercise 27.2 Question 25 Maths Textbook Solution.

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Answer: the value of k will be ‘2

Given: find the value of k so that the lines x-y=kz \: and \: \: x-2y=2y+1 = -z+1 are perpendicular to each other.

Hint: when two lines are perpendicular then dot product will be equal to ‘0

Solution: from equ (i)

             x=y=kz=\frac{x}{1}=\frac{y}{-1}=\frac{3}{1/k}

From equation (ii)

                \frac{x-2}{1}=\frac{y+1/2}{1/2}=\frac{z-1}{-1}

Since two straight lines are perpendicular to each other then

\begin{aligned} &a_{1} a_{2}+b_{1} b_{2}+c_{1} c_{2}=0 \\\\ &(1)+(-1 / 2)+(-1 / k)=0 \\\\ &\frac{2-1}{2}=\frac{1}{k} \\\\ &1 / 2=1 / \mathrm{k} \\\\ &\mathrm{K} \quad=2 \end{aligned}

 

                So the answer will be ‘2

 

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