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If alpha(axxb)+beta(bxxc)+gamma(cxxa)=0,...

If `alpha(axxb)+beta(bxxc)+gamma(cxxa)=0`, then

A

a,b,c are coplanar if all of `alpha,beta,gamma ne0`

B

a,b,c are coplanar if any one of `alpha,beta,gammane0`

C

a,b,c are non-coplanar for any `alpha,beta,gammane0`

D

none of these

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To solve the problem given by the equation \( \alpha ( \mathbf{a} \times \mathbf{b}) + \beta ( \mathbf{b} \times \mathbf{c}) + \gamma ( \mathbf{c} \times \mathbf{a}) = 0 \), we need to analyze the implications of this vector equation. ### Step-by-step Solution: 1. **Understanding the Vector Equation**: The equation states that a linear combination of the cross products of vectors \( \mathbf{a}, \mathbf{b}, \) and \( \mathbf{c} \) equals the zero vector. This implies that the vectors are linearly dependent. **Hint**: Recall that if a linear combination of vectors equals zero, the vectors must be coplanar. 2. **Using the Scalar Triple Product**: We can express the cross products in terms of the scalar triple product. The scalar triple product \( [\mathbf{a}, \mathbf{b}, \mathbf{c}] \) (or \( \text{box}( \mathbf{a}, \mathbf{b}, \mathbf{c}) \)) is defined as \( \mathbf{a} \cdot (\mathbf{b} \times \mathbf{c}) \). 3. **Analyzing Each Case**: - **Case 1**: Assume \( \alpha, \beta, \gamma \) are all non-zero. If \( \alpha, \beta, \gamma \neq 0 \), then the equation can be rearranged to show that the scalar triple product must equal zero for the equation to hold: \[ \alpha (\mathbf{a} \times \mathbf{b}) + \beta (\mathbf{b} \times \mathbf{c}) + \gamma (\mathbf{c} \times \mathbf{a}) = 0 \] implies that \( [\mathbf{a}, \mathbf{b}, \mathbf{c}] = 0 \), indicating that \( \mathbf{a}, \mathbf{b}, \mathbf{c} \) are coplanar. **Hint**: If the coefficients are all non-zero and the sum is zero, the vectors must be coplanar. 4. **Case 2**: If any one of \( \alpha, \beta, \gamma \) is non-zero, the same reasoning applies. For instance, if \( \alpha \neq 0 \), we can rearrange the equation to isolate the term involving \( \alpha \): \[ \alpha (\mathbf{a} \times \mathbf{b}) = -(\beta (\mathbf{b} \times \mathbf{c}) + \gamma (\mathbf{c} \times \mathbf{a})) \] This indicates that the left side must also yield a vector that is dependent on the right side, reinforcing that the vectors are coplanar. **Hint**: If at least one coefficient is non-zero, the vectors remain dependent, and thus coplanar. 5. **Case 3**: If all coefficients are zero, the equation trivially holds, but this does not provide any information about the coplanarity of the vectors. 6. **Conclusion**: - **Option A**: \( \mathbf{a}, \mathbf{b}, \mathbf{c} \) are coplanar if all of \( \alpha, \beta, \gamma \) are non-zero. **Correct**. - **Option B**: \( \mathbf{a}, \mathbf{b}, \mathbf{c} \) are coplanar if any one of \( \alpha, \beta, \gamma \) is non-zero. **Correct**. - **Option C**: \( \mathbf{a}, \mathbf{b}, \mathbf{c} \) are non-coplanar for any \( \alpha, \beta, \gamma \) not equal to zero. **Incorrect**. - **Option D**: None of these. **Incorrect**. Thus, the correct options are A and B. ### Final Answer: Options A and B are correct.
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ARIHANT MATHS ENGLISH-PRODUCT OF VECTORS-Exercise (Questions Asked In Previous 13 Years Exam)
  1. If alpha(axxb)+beta(bxxc)+gamma(cxxa)=0, then

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  2. Let O be the origin and let PQR be an arbitrary triangle. The point S ...

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  3. Let O be the origin and vec(OX) , vec(OY) , vec(OZ) be three unit vec...

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  4. Let O be the origin, and O X , O Y , O Z be three unit vectors ...

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  5. Let a, b and c be three unit vectors such that atimes(btimesc)=(sqrt(3...

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  6. Let vec a , vec b and vec c be three non-zero vectors such that no ...

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  7. If vec a , vec ba n d vec c are unit vectors satisfying | vec a- v...

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  8. The vector(s) which is/are coplanar with vectors hat i+ hat j+2 hat...

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  9. Let vec a= hat i+ hat j+ hat k , vec b= hat i- hat j+ hat ka n d vec ...

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  10. Two adjacent sides of a parallelogram A B C D are given by vec A B=...

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  11. Let P,Q R and S be the points on the plane with position vectors -2hat...

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  12. If aa n db are vectors in space given by vec a=( hat i-2 hat j)/(sq...

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  13. If veca,vecb,vecc and vecd are unit vectors such that (vecaxxvecb)*(...

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  14. The edges of a parallelopiped are of unit length and are parallel to ...

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  15. Let two non-collinear unit vectors veca and vecb form an acute angle. ...

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  16. Let the vectors PQ,OR,RS,ST,TU and UP represent the sides of a regular...

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  17. The number of distinct real values of lambda , for which the vectors...

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  18. Let veca,vecb,vecc be unit vectors such that veca+vecb+vecc=vec0. Whic...

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  19. Let vec A be a vector parallel to the line of intersection of plan...

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  20. Let vec a= hat i+2 hat j+ hat k , vec b= hat i- hat j+ hat ka n d vec...

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  21. The unit vector which is orthogonal to the vector 3hati+2hatj+6hatk an...

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