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Prove that the Following Vectors Are Coplanar: 2 ^ I − ^ J + ^ K , ^ I − 3 ^ J − 5 ^ K and 3 ^ I − 4 ^ J − 4 ^ K - Mathematics

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प्रश्न

Prove that the following vectors are coplanar:
\[2 \hat{i} - \hat{j} + \hat{k} , \hat{i} - 3 \hat{j} - 5 \hat{k} \text{ and }3 \hat{i} - 4 \hat{j} - 4 \hat{k}\]

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उत्तर

Given the vectors

\[P\left( 2 \hat{i} - \hat{j} + \hat{k} \right), Q\left( \hat{i} - 3 \hat{j} - 5 \hat{k} \right)\] and \[R\left( 3 \hat{i} - 4 \hat{j} - 4 \hat{k} \right)\] 
 We know the three vectors are coplanar if one of them is expressible as a linear combination of the other two.
Let, \[2 \hat{i} - \hat{j} + \hat{k} = x \left( \hat{i} - 3 \hat{j} - 5 \hat{k} \right) + y \left( 3 \hat{i} - 4 \hat{j} - 4 \hat{k} \right) . \]
\[ = \hat{i} \left( x + 3y \right) + \hat{j} \left( - 3x - 4y \right) + \hat{k} \left( - 5x - 4y \right) .\]
\[\Rightarrow x + 3y = 2, - 3x - 4y = - 1, - 5x - 4y = 1\]                            [Equating the coefficients of \[\hat{i} , \hat{j} , \hat{k}\] respectively]
Solving first two of these equation, we get \[x = - 1 , y = 1\]. Clearly these two values satisfy the third equation.
Hence, the given vectors are coplanar.
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अध्याय 23: Algebra of Vectors - Exercise 23.8 [पृष्ठ ६५]

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आरडी शर्मा Mathematics [English] Class 12
अध्याय 23 Algebra of Vectors
Exercise 23.8 | Q 5.1 | पृष्ठ ६५

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