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Let veca=2hati+3hatj-hatk and vecb=hati-...

Let `veca=2hati+3hatj-hatk` and `vecb=hati-2hatj+3hatk`. Then , the value of `lamda` for which the vector `vecc=lamdahati+hatj+(2lamda-1)hatk` is parallel to the plane containing `veca` and `vecb`. Is

A

`1`

B

`0`

C

`-1`

D

`2`

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The correct Answer is:
To solve the problem, we need to find the value of \( \lambda \) for which the vector \( \vec{c} = \lambda \hat{i} + \hat{j} + (2\lambda - 1) \hat{k} \) is parallel to the plane containing the vectors \( \vec{a} = 2\hat{i} + 3\hat{j} - \hat{k} \) and \( \vec{b} = \hat{i} - 2\hat{j} + 3\hat{k} \). ### Step 1: Understand the condition for parallelism A vector \( \vec{c} \) is parallel to the plane formed by two vectors \( \vec{a} \) and \( \vec{b} \) if it is perpendicular to the cross product \( \vec{a} \times \vec{b} \). This means that \( \vec{c} \cdot (\vec{a} \times \vec{b}) = 0 \). ### Step 2: Calculate the cross product \( \vec{a} \times \vec{b} \) We can calculate \( \vec{a} \times \vec{b} \) using the determinant of a matrix formed by the unit vectors \( \hat{i}, \hat{j}, \hat{k} \) and the components of \( \vec{a} \) and \( \vec{b} \): \[ \vec{a} \times \vec{b} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 2 & 3 & -1 \\ 1 & -2 & 3 \end{vmatrix} \] ### Step 3: Compute the determinant Calculating the determinant, we have: \[ \vec{a} \times \vec{b} = \hat{i} \begin{vmatrix} 3 & -1 \\ -2 & 3 \end{vmatrix} - \hat{j} \begin{vmatrix} 2 & -1 \\ 1 & 3 \end{vmatrix} + \hat{k} \begin{vmatrix} 2 & 3 \\ 1 & -2 \end{vmatrix} \] Calculating each of these 2x2 determinants: 1. For \( \hat{i} \): \[ 3 \cdot 3 - (-1) \cdot (-2) = 9 - 2 = 7 \] 2. For \( \hat{j} \): \[ 2 \cdot 3 - (-1) \cdot 1 = 6 + 1 = 7 \] 3. For \( \hat{k} \): \[ 2 \cdot (-2) - 3 \cdot 1 = -4 - 3 = -7 \] Putting it all together, we get: \[ \vec{a} \times \vec{b} = 7\hat{i} - 7\hat{j} - 7\hat{k} = 7(\hat{i} - \hat{j} - \hat{k}) \] ### Step 4: Set up the dot product equation Now, we need to find \( \lambda \) such that: \[ \vec{c} \cdot (\vec{a} \times \vec{b}) = 0 \] Substituting \( \vec{c} \) and \( \vec{a} \times \vec{b} \): \[ (\lambda \hat{i} + \hat{j} + (2\lambda - 1) \hat{k}) \cdot (7\hat{i} - 7\hat{j} - 7\hat{k}) = 0 \] Calculating the dot product: \[ 7\lambda - 7 + (-7)(2\lambda - 1) = 0 \] Expanding this: \[ 7\lambda - 7 - 14\lambda + 7 = 0 \] Combining like terms: \[ -7\lambda = 0 \] ### Step 5: Solve for \( \lambda \) Thus, we find: \[ \lambda = 0 \] ### Final Answer The value of \( \lambda \) for which the vector \( \vec{c} \) is parallel to the plane containing \( \vec{a} \) and \( \vec{b} \) is \( \lambda = 0 \). ---

To solve the problem, we need to find the value of \( \lambda \) for which the vector \( \vec{c} = \lambda \hat{i} + \hat{j} + (2\lambda - 1) \hat{k} \) is parallel to the plane containing the vectors \( \vec{a} = 2\hat{i} + 3\hat{j} - \hat{k} \) and \( \vec{b} = \hat{i} - 2\hat{j} + 3\hat{k} \). ### Step 1: Understand the condition for parallelism A vector \( \vec{c} \) is parallel to the plane formed by two vectors \( \vec{a} \) and \( \vec{b} \) if it is perpendicular to the cross product \( \vec{a} \times \vec{b} \). This means that \( \vec{c} \cdot (\vec{a} \times \vec{b}) = 0 \). ### Step 2: Calculate the cross product \( \vec{a} \times \vec{b} \) We can calculate \( \vec{a} \times \vec{b} \) using the determinant of a matrix formed by the unit vectors \( \hat{i}, \hat{j}, \hat{k} \) and the components of \( \vec{a} \) and \( \vec{b} \): ...
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OBJECTIVE RD SHARMA ENGLISH-SCALAR AND VECTOR PRODUCTS OF THREE VECTORS -Section I - Solved Mcqs
  1. If vecrxxvecb=veccxxvecb and vecr|veca then vecr is equal to

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  2. If veca, vecb, vecc are any three vectors such that (veca+vecb).vecc=(...

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  3. Let veca=2hati+3hatj-hatk and vecb=hati-2hatj+3hatk. Then , the value ...

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  4. Let veca, vecb, vecc be three unit vectors such that veca. vecb=veca.v...

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  5. If veca, vecb, vecc are three non coplanar, non zero vectors then (vec...

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  6. If the acute angle that the vector alphahati+betahatj+gammahatk makes ...

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  7. If veca,vecb,vecc are three non-coplanar vectors and vecp,vecq,vecr ar...

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  8. If veca vecb are non zero and non collinear vectors, then [(veca, vecb...

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  9. If vecr is a unit vector such that vecr=x(vecbxxvecc)+y(veccxxveca)+...

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  10. Let a,b,c be three vectors such that [a b c]=2, if r=l(bxxc)+m(cxxa)+n...

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  11. If vecb is a unit vector, then (veca. vecb)vecb+vecbxx(vecaxxvecb) is ...

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  12. If veca, vecb, vecc are any three non coplanar vectors, then [(veca+ve...

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  13. If veca, vecb, vecc are any three non coplanar vectors, then (veca+v...

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  14. Let veca, vecb and vecc be three having magnitude 1,1 and 2 respective...

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  15. If veca = (hati + hatj +hatk), veca. vecb= 1 and vecaxxvecb = hatj -ha...

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  16. If veca, vecb, vecc are non-coplanar non-zero vectors, then (vecaxxv...

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  17. If the vectors veca, vecb, vecc and vecd are coplanar vectors, then (...

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  18. (vecaxxvecb).(veccxxvecd) is not equal to

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  19. Let veca = 2hati + hatj + hatk, and vecb = hati+ hatj if c is a vecto...

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  20. If veca,vecb and vecc are three non coplanar vectors and vecr is any v...

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