Question Details

Let α and β be the distinct roots of the equation x 2 + x 1 = 0 . Consider the set T = {1, α, β}. For a 3 x 3 matrix M = ( a i j ) 3 × 3 ) , define R i a i 1 + a i 2 + a i 3  and C j = a 1 j + a 2 j + a 3 j 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  ( a i j ) 3 × 3 with
all entries in T such that Ri = Cj = 0
for all i, j is  
(1) 1
(Q) The number of symmetric matrices

( a i j ) 3 × 3 with all entries in T such that
Cj = 0 for all j, is
(2) 12
(R) Let  ( a i j ) 3 × 3  be a skew symmetric
matrix such that  a i j  ∈ T for i > j. Then
the number of elements in the set

{ ( x y z ) : x , y z R , M ( x y z ) = ( a 12 0 a 23 ) }
(3) infinite
(S) Let  ( a i j ) 3 × 3  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

Options

A

(P) → (4)  (Q) → (2)  (R) → (5)  (S) → (1)

B

(P) → (2)  (Q) → (4)  (R) → (1)  (S) → (5)

C

(P) → (2)  (Q) → (4)  (R) → (3)  (S) → (5)

D

(P) → (1)  (Q) → (5)  (R) → (3)  (S) → (4)

Show Answer

Correct Answer :

Option C

(P) → (2)  (Q) → (4)  (R) → (3)  (S) → (5)

(P) → (2) (Q) → (4) (R) → (3) (S) → (5)

Solution :

Given Equation and Set T:
The quadratic equation is given by:
x 2 + x - 1 = 0
Since �� and β are the distinct roots of this equation, we have:
α + β = - 1
This implies:
1 + α + β = 0
The roots of the equation are approximately α0.618 and β-1.618. The set is T={1,α,β}. Since 1, α, and β are distinct real numbers, the only way a sum of three elements from T (with repetitions allowed) equals zero is if the three elements are exactly 1, α, and β in some order.

Analysis of (P):
We want to find the number of matrices M=(aij)3×3 with entries in T such that Ri=Cj=0 for all i,j.
Since the sum of elements in each row and column is zero, each row and column must contain the elements 1, α, and β exactly once. This is the definition of a Latin square of order 3.
- For the first row, there are 3!=6 permutations.
- Once the first row is chosen (say, A,B,C), the remaining elements must satisfy the Latin square property. There are exactly 2 valid arrangements for the second and third rows:
Either:
Row 2: B,C,A and Row 3: C,A,B
Or:
Row 2: C,A,B and Row 3: B,C,A
Therefore, the total number of such matrices is:
6 × 2 = 12
Thus, (P) → (2).

Analysis of (Q):
We need to find the number of symmetric matrices M=(aij)3×3 with all entries in T such that Cj=0 for all j.
Since M is symmetric, Ri=Ci=0 for all i. Thus, it must also form a Latin square.
Let the symmetric Latin square be:
( A B C B d e C e f )
For this matrix to be a Latin square:
- Row 2 requires {B,d,e}={A,B,C}{d,e}={A,C}
- Row 3 requires {C,e,f}={A,B,C}{e,f}={A,B}
Comparing the two, we must have e=A.
This uniquely determines d=C and f=B.
Thus, for each of the 6 permutations of the first row, there is exactly 1 symmetric matrix:
( A B C B C A C A B )
So the total number of symmetric matrices is 6.
Thus, (Q) → (4).

Analysis of (R):
Let M=(aij)3×3 be a skew-symmetric matrix. Therefore, the diagonal entries are zero (a11=a22=a33=0) and aji=-aij.
The matrix M is:
M = ( 0 a12 a13 -a12 0 a23 -a13 -a23 0 )
We are given the system:
M ( x y z ) = ( a12 0 -a23 )
This gives the following system of linear equations:
1) a12y+a13z=a12
2) -a12x+a23z=0x=a23a12z
3) -a13x-a23y=-a23
From (1), we get:
y = 1 - a13a12z
Substituting x and y into (3):
- a 13 ( a 23 a 12 z ) - a 23 ( 1 - a 13 a 12 z ) = - a 23
- a 13 a 23 a 12 z - a 23 + a 13 a 23 a 12 z = - a 23
- a 23 = - a 23
This is an identity that is always satisfied, independent of the value of z. Therefore, for any real value z, there is a unique pair of values for x and y. Hence, the system has an infinite number of solutions.
Thus, (R) → (3).

Analysis of (S):
We are given that Ri=0 for all i, which means:
ai1 + ai2 + ai3 = 0
for i=1,2,3.
If we perform the column operation C1C1+C2+C3 on the matrix M, the first column of the resulting determinant becomes:
( a11+a12+a13 a21+a22+a23 a31+a32+a33 ) = ( 0 0 0 )
Since an entire column consists of zeros, the determinant is 0, and its absolute value is also 0.
Thus, (S) → (5).

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