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Find the Angle Between the Following Pairs of Lines: → R = ( 3 ^ I + 2 ^ J − 4 ^ K ) + λ ( ^ I + 2 ^ J + 2 ^ K ) and → R = ( 5 ^ J − 2 ^ K ) + μ ( 3 ^ I + 2 ^ J + 6 ^ K )

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प्रश्न

Find the angle between the following pair of line: 

\[\overrightarrow{r} = \left( 3 \hat{i} + 2 \hat{j} - 4 \hat{k} \right) + \lambda\left( \hat{i} + 2 \hat{j} + 2 \hat{k} \right) \text{ and } \overrightarrow{r} = \left( 5 \hat{j} - 2 \hat{k}  \right) + \mu\left( 3 \hat{i} + 2 \hat{j} + 6 \hat{k} \right)\]

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उत्तर

\[\overrightarrow{r} = \left( 3 \hat{i} + 2 \hat{j} - 4 \hat{k} \right) + \lambda\left( \hat{i} + 2 \hat{j} + 2 \hat{k} \right) \text{ and } \overrightarrow{r} = \left( 5 \hat{j} - 2 \hat{k}  \right) + \mu\left( 3 \hat{i} + 2 \hat{j} + 6 \hat{k} \right)\] 

Let

\[\overrightarrow{b_1} \text{ and } \overrightarrow{b_2}\]  be vector parallel to the given line.

Now,

\[\overrightarrow{b_1} = \hat{i} + 2 \hat{j} + 2 \hat{k} \]

\[ \overrightarrow{b_2} = 3 \hat{i} + 2 \hat{j} + 6 \hat{k} \]

If θ is the angle between the given line, then

\[\cos \theta = \frac{\overrightarrow{b_1} . \overrightarrow{b_2}}{\left| \overrightarrow{b_1} \right| \left| \overrightarrow{b_2} \right|}\]

\[ = \frac{\left( \hat{i} + 2 \hat{j} + 2 \hat{k} \right) . \left( 3 \hat{i} + 2 \hat{j} + 6 \hat{k} \right)}{\sqrt{1^2 + 2^2 + 2^2} \sqrt{3^2 + 2^2 + 6^2}}\]

\[ = \frac{3 + 4 + 12}{3 \times 7}\]

\[ = \frac{19}{21}\]

\[ \Rightarrow \theta = \cos^{- 1} \left( \frac{19}{21} \right)\]

 

 

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अध्याय 27: Straight Line in Space - Exercise 28.2 [पृष्ठ १६]

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आर.डी. शर्मा Mathematics Volume 1 and 2 [English] Class 12
अध्याय 27 Straight Line in Space
Exercise 28.2 | Q 8.2 | पृष्ठ १६

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