Let α and β be the distinct roots of the equation . Consider the set T = {1, α, β}. For a 3 x 3 matrix , define = and = for i = 1, 2, 3 and j = 1, 2, 3.
Match each entry in List-I to the correct entry in List-II.
| List -I | List -II |
| (P) The number of matrices with all entries in T such that Ri = Cj = 0 for all i, j is |
(1) 1 |
| (Q) The number of symmetric matrices with all entries in T such that Cj = 0 for all j, is |
(2) 12 |
| (R) Let be a skew symmetric matrix such that ∈ T for i > j. Then the number of elements in the set |
(3) infinite |
| (S) Let be a matrix with all entries in T such that Ri = 0 for all i. Then the absolute value of the determinant of M is |
(4) 6 |
| (5) 0 |
The correct option is
Correct Answer :
(P) → (2) (Q) → (4) (R) → (3) (S) → (5)
Solution :
Given Equation and Set T:
The quadratic equation is given by:
Since and are the distinct roots of this equation, we have:
This implies:
The roots of the equation are approximately and .
The set is .
Since , , and are distinct real numbers, the only way a sum of three elements from (with repetitions allowed) equals zero is if the three elements are exactly , , and in some order.
Analysis of (P):
We want to find the number of matrices with entries in such that for all .
Since the sum of elements in each row and column is zero, each row and column must contain the elements , , and exactly once. This is the definition of a Latin square of order 3.
- For the first row, there are permutations.
- Once the first row is chosen (say, ), the remaining elements must satisfy the Latin square property. There are exactly 2 valid arrangements for the second and third rows:
Either:
Row 2: and Row 3:
Or:
Row 2: and Row 3:
Therefore, the total number of such matrices is:
Thus, (P) → (2).
Analysis of (Q):
We need to find the number of symmetric matrices with all entries in such that for all .
Since is symmetric, for all . Thus, it must also form a Latin square.
Let the symmetric Latin square be:
For this matrix to be a Latin square:
- Row 2 requires
- Row 3 requires
Comparing the two, we must have .
This uniquely determines and .
Thus, for each of the permutations of the first row, there is exactly symmetric matrix:
So the total number of symmetric matrices is .
Thus, (Q) → (4).
Analysis of (R):
Let be a skew-symmetric matrix. Therefore, the diagonal entries are zero () and .
The matrix is:
We are given the system:
This gives the following system of linear equations:
1)
2)
3)
From (1), we get:
Substituting and into (3):
This is an identity that is always satisfied, independent of the value of . Therefore, for any real value , there is a unique pair of values for and .
Hence, the system has an infinite number of solutions.
Thus, (R) → (3).
Analysis of (S):
We are given that for all , which means:
for .
If we perform the column operation on the matrix , the first column of the resulting determinant becomes:
Since an entire column consists of zeros, the determinant is , and its absolute value is also .
Thus, (S) → (5).
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