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Explain Solution R.D.Sharma Class 12 Chapter 27 Straight Line in Space Exercise 27.2 Question 26 Maths Textbook Solution.

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Answer: the required vector equation is \vec{r}=(\hat{i}+\hat{j}+\hat{k})+\lambda(-4 \hat{i}+4 \hat{j}-\hat{k})

 

Given: find the vector and Cartesian equation of the line which is perpendicular to the lines with the equation

\frac{x+2}{1}=\frac{y-3}{2}=\frac{z+1}{2}and \: \frac{x-1}{2}=\frac{y-2}{3}

                =         \frac{z-3}{4}     and passes through the points (1,1,1). Also find the angle between the given lines

Hint: for showing perpendicular dot product must be equal to ‘0

Solution: let the cartesian equation of the line passing through the point (1,1,1) will be

\frac{x-1}{a}=\frac{y-1}{b}=\frac{z-1}{c}

Now parallel vectors are  \bar{b_{1}},\bar{b_{2}},\bar{b_{3}}                                                                                                                                                       

From the question,

 \begin{aligned} &\vec{b}_{1}=\hat{a} \hat{i}+b \hat{j}+c \hat{k} \\ &\overrightarrow{b_{2}}=\hat{i}+2 \hat{j}+4 \hat{k} \text { Here } \\ &\overrightarrow{b_{3}}=2 \hat{i}+3 \hat{j}+4 \hat{k} \end{aligned}

                 \begin{aligned} &a+2 b+4 c=0 \ldots .(\mathrm{lV}) \\ &2 a+3 b+4 c=0 \ldots \ldots(\mathrm{V}) \end{aligned}

                  Solving (iv) and (v) we get

                   \begin{aligned} &\frac{a}{8-12}=\frac{b}{8-4}=\frac{c}{3-4} \\ &\therefore \frac{a}{-4}=\frac{b}{4}=\frac{c}{-1}=\lambda \end{aligned} 

               Therefore a=4\lambda ,b=4\lambda ,c=-\lambda

Now putting the above makes in equation;

  \begin{aligned} &\frac{x-1}{-4 \lambda}=\frac{y-1}{4 \lambda}=\frac{z-1}{-\lambda} \\ &\frac{x-1}{-4}=\frac{y-1}{4}=\frac{z-1}{-1} \end{aligned}           hence the vector equation is \vec{r}=(\hat{i}+\hat{j}+\hat{k})+\lambda(-4 \hat{i}+4 \hat{j}-\hat{k}).

 

 

 

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