Let A be a 3 × 3 real matrix such that A(\matrix1\cr1\cr0\cr)=(\matrix1\cr1\cr0\cr);A(\matrix1\cr0\cr1\cr)=(\matrix−1\cr0\cr1\cr) and A(\matrix0\cr0\cr1\cr)=(\matrix1\cr1\cr2\cr). If X=(x1,x2,x3)T and I is an identity matrix of order 3, then the system (A−2I)X=(\matrix4\cr1\cr1\cr) has :
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Solution
This problem requires us to determine the nature of solutions for a system of linear equations (A−2I)X=B. The core concept lies in analyzing the determinant and rank of the coefficient matrix (A−2I).
Key Concepts for Systems of Linear Equations CX=B:
For a system of linear equations CX=B, where C is a square matrix of order n:
Unique Solution: If det(C)=0, then the matrix C is invertible, and a unique solution X=C−1B exists.
No Solution or Infinitely Many Solutions: If det(C)=0, then the matrix C is singular. In this case, we need to check the consistency of the system using the concept of rank:
If rank(C)=rank([C∣B])<n (where [C∣B] is the augmented matrix), the system is consistent and has infinitely many solutions. This occurs when the right-hand side vector B can be expressed as a linear combination of the column vectors of C, and there are free variables.
If rank(C)=rank([C∣B]), the system is inconsistent and has no solution. This occurs when the right-hand side vector B cannot be expressed as a linear combination of the column vectors of C.
Our strategy will be:
First, determine the matrix A using the given conditions.
Then, calculate the coefficient matrix C=(A−2I).
Calculate det(C).
If det(C)=0, we will analyze the system (A−2I)X=B directly to check for consistency and determine if there are no solutions or infinitely many solutions.
Step 1: Determining the Matrix A
Let the 3x3 matrix A be represented as:
A=adgbehcfi
We are given three conditions involving matrix A and specific column vectors:
Condition 1:A110=110
Performing the matrix multiplication:
adgbehcfi110=a(1)+b(1)+c(0)d(1)+e(1)+f(0)g(1)+h(1)+i(0)=a+bd+eg+h
Equating this to the given result:
a+bd+eg+h=110⇒⎩⎨⎧a+b=1d+e=1g+h=0(Eq. 1.1)(Eq. 1.2)(Eq. 1.3)
Condition 2:A101=−101
Performing the matrix multiplication:
adgbehcfi101=a(1)+b(0)+c(1)d(1)+e(0)+f(1)g(1)+h(0)+i(1)=a+cd+fg+i
Equating this to the given result: