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Explain Solution R.D.Sharma Class 12 Chapter 27 Straight Line in Space Exercise 27.2 Question 24 Maths Textbook Solution.

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Answer : the direction cosines will be \frac{2}{7},\frac{3}{7},\frac{-6}{7} and the equation will be \vec{r}=\left ( \hat{i}-2\hat{j}+3\hat{k} \right )+\lambda \left ( 2\hat{i}+3\hat{j}-6\hat{k} \right )

Given: find the direction cosines of the lines \frac{x+2}{2}=\frac{2y-7}{6}=\frac{5-z}{6} and also find the vector equation of the line through the point (-1,2,3) and parallel to the given line

Hint:

Solution: \frac{x+2}{2}=\frac{y-7/2}{3}=\frac{z-5}{-6}

Direction ratio =2,3,-6

Direction cosines =  \frac{2}{\sqrt{49}}=\frac{3}{\sqrt{49}}=\frac{6}{\sqrt{49}}

\mathrm{DC}=\frac{a}{\sqrt{a^{2}+b^{2}+c^{2}}}, \frac{b}{\sqrt{a^{2}+b^{2}+c^{2}}},=\frac{2}{7}, \frac{3}{7}, \frac{-6}{7}, \frac{c}{\sqrt{a^{2}+b^{2}+c^{2}}}

Now, vector along the line; 2\hat{i}+3\hat{j}-6\hat{k}

\vec{r}=\hat{i}-2\hat{j}+3\hat{k} +\lambda \left ( 2\hat{i}+3\hat{j}-6\hat{k} \right )

So the answer will be

\vec{r}=\hat{i}-2\hat{j}+3\hat{k} +\lambda \left ( 2\hat{i}+3\hat{j}-6\hat{k} \right ) and cosines will be \frac{2}{7},\frac{3}{7},\frac{-6}{7}

 

 

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