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Consider the determinant, Delta=|(p,q,r)...

Consider the determinant, `Delta=|(p,q,r),(x,y,z),(l,m,n)|` .
`M_(ij)` denotes the minor of an element in `i^(th)` row, and `j^(th)` column
`C_(ij)` denotes the cofactor of an element in `i^(th)` row and `j^(th)` column
the value of `q.M_12 - y.M_22+ m.M_32` is :

A

0

B

`-Delta`

C

`Delta`

D

`Delta^2`

Text Solution

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The correct Answer is:
To solve the problem, we need to find the value of the expression \( q \cdot M_{12} - y \cdot M_{22} + m \cdot M_{32} \), where \( M_{ij} \) denotes the minor of the element in the \( i^{th} \) row and \( j^{th} \) column of the determinant \( \Delta = \begin{vmatrix} p & q & r \\ x & y & z \\ l & m & n \end{vmatrix} \). ### Step 1: Calculate the minors \( M_{12}, M_{22}, \) and \( M_{32} \) 1. **Finding \( M_{12} \)**: - The minor \( M_{12} \) is obtained by deleting the first row and second column of the determinant. - The remaining elements are: \[ \begin{vmatrix} x & z \\ l & n \end{vmatrix} = x \cdot n - z \cdot l \] - Thus, \( M_{12} = xn - zl \). 2. **Finding \( M_{22} \)**: - The minor \( M_{22} \) is obtained by deleting the second row and second column of the determinant. - The remaining elements are: \[ \begin{vmatrix} p & r \\ l & n \end{vmatrix} = p \cdot n - r \cdot l \] - Thus, \( M_{22} = pn - lr \). 3. **Finding \( M_{32} \)**: - The minor \( M_{32} \) is obtained by deleting the third row and second column of the determinant. - The remaining elements are: \[ \begin{vmatrix} p & q \\ x & z \end{vmatrix} = p \cdot z - q \cdot x \] - Thus, \( M_{32} = pz - qx \). ### Step 2: Substitute the minors into the expression Now we substitute \( M_{12}, M_{22}, \) and \( M_{32} \) into the expression \( q \cdot M_{12} - y \cdot M_{22} + m \cdot M_{32} \): \[ q \cdot M_{12} - y \cdot M_{22} + m \cdot M_{32} = q(xn - zl) - y(pn - lr) + m(pz - qx) \] ### Step 3: Expand the expression Expanding the expression gives: \[ = qxn - qzl - ypn + ylr + mpz - mqx \] ### Step 4: Rearranging the expression Rearranging the terms, we get: \[ = qxn - mqx - ypn + ylr + mpz - qzl \] ### Step 5: Compare with the determinant Now, we can compare this expression with the determinant \( \Delta = \begin{vmatrix} p & q & r \\ x & y & z \\ l & m & n \end{vmatrix} \). The determinant can be calculated as: \[ \Delta = p(y \cdot n - z \cdot m) - q(x \cdot n - z \cdot l) + r(x \cdot m - y \cdot l) \] Upon careful observation, we can see that the expression we derived is actually the negative of the determinant \( \Delta \). ### Conclusion Thus, we conclude that: \[ q \cdot M_{12} - y \cdot M_{22} + m \cdot M_{32} = -\Delta \] The final answer is: \[ \text{Value} = -\Delta \]
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