मराठी

The Shortest Distance Between the Lines X − 3 3 = Y − 8 − 1 = Z − 3 1 a N D , X + 3 − 3 = Y + 7 2 = Z − 6 4 (A) √ 30 (B) 2 √ 30 (C) 5 √ 30 (D) 3 √ 30 - Mathematics

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प्रश्न

The shortest distance between the lines  \[\frac{x - 3}{3} = \frac{y - 8}{- 1} = \frac{z - 3}{1} \text{ and }, \frac{x + 3}{- 3} = \frac{y + 7}{2} = \frac{z - 6}{4}\] 

 

 

 

 

पर्याय

  •  \[\sqrt{30}\] 

  • \[2\sqrt{30}\] 

  • \[5\sqrt{30}\] 

  •  \[3\sqrt{30}\] 

MCQ
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उत्तर

 \[3\sqrt{30}\]

We have ,

\[\frac{x - 3}{3} = \frac{y - 8}{- 1} = \frac{z - 3}{1} . . . (1) \]

\[\frac{x + 3}{- 3} = \frac{y + 7}{2} = \frac{z - 6}{4} . . . (2)\] 

We know that line (1) passes through the point (3, 8, 3) and has direction ratios proportional to 3,-1 , 1 . 

Its vector equation is , 

\[\overrightarrow{r} = \overrightarrow{a_1} + \lambda \overrightarrow{b_1} , \text{ where }\overrightarrow{a_1} = 3 \hat{i} + 8 \hat{j} + 3 \hat{k}  \text{ and }  \overrightarrow{b_1} = 3 \hat{i}  - \hat{j}  + \hat{k}  .\] 

Also, line (2) passes through the point ( -3 , -7 , 6 )  and has direction ratios proportional to -3, 2 4 . 

Its vector equation is

\[\overrightarrow{r} = \overrightarrow{a_2} + \mu \overrightarrow{b_2} , \text{ where } \overrightarrow{a_2} = - 3 \hat{i} - 7 \hat{j} + 6 \hat{k} \text{ and }  \overrightarrow{b_2} = - 3 \hat{i} + 2 \hat{j}  + 4 \hat{k}  .\]

Now, 

\[\overrightarrow{a_2} - \overrightarrow{a_1} = - 6 \hat{i} - 15 \hat{j} + 3 \hat{k} \]

\[ \overrightarrow{b_1} \times \overrightarrow{b_2} = \begin{vmatrix}\hat{i} & \hat{j} & \hat{k}  \\ 3 & - 1 & 1 \\ - 3 & 2 & 4\end{vmatrix}\]

\[ = - 6 \hat{i} - 15 \hat{j} + 3 \hat{k}  \]

\[ \Rightarrow \left| \overrightarrow{b_1} \times \overrightarrow{b_2} \right| = \sqrt{\left( - 6 \right)^2 + \left( - 15 \right)^2 + 3^2}\]

\[ = \sqrt{36 + 225 + 9}\]

\[ = \sqrt{270}\]

\[\left( \overrightarrow{a_2} - \overrightarrow{a_1} \right) . \left( \overrightarrow{b_1} \times \overrightarrow{b_2} \right) = \left( - 6 \hat{i} - 15 \hat{j} + 3 \hat{k} \right) . \left( - 6 \hat{i}  - 15 \hat{j}  + 3 \hat{k}  \right)\]

\[ = 36 + 225 + 9\]

\[ = 270\] 

The shortest distance between the lines 

\[\overrightarrow{r} = \overrightarrow{a_1} + \lambda \overrightarrow{b_1} \text{ and }  \overrightarrow{r} = \overrightarrow{a_2} + \mu \overrightarrow{b_2}\]  is given by 

\[d = \left| \frac{\left( \overrightarrow{a_2} - \overrightarrow{a_1} \right) . \left( \overrightarrow{b_1} \times \overrightarrow{b_2} \right)}{\left| \overrightarrow{b_1} \times \overrightarrow{b_2} \right|} \right|\]

\[ = \left| \frac{270}{\sqrt{270}} \right|\]

\[ = \sqrt{270}\]

\[ = 3\sqrt{30}\]

 

 

 

 

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पाठ 28: Straight Line in Space - MCQ [पृष्ठ ४३]

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आरडी शर्मा Mathematics [English] Class 12
पाठ 28 Straight Line in Space
MCQ | Q 14 | पृष्ठ ४३

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