JEE MainMathematicsMatrices and DeterminantsMCQ+4 / −1
If the system of linear equations has infinitely many solutions, then the value of is :
- A31
- B37
- C43
- D49
View written solutionFree
Correct answer: A
-
For the system to have infinitely many solutions, we need:
- The coefficient matrix to be singular:
- And the system to be consistent, i.e. ranks of coefficient and augmented matrices must be equal and less than 3.
The system is
3x+y+\beta z&=3 \\ 2x+\alpha y-z&=-3 \\ x+2y+z&=4 \end{aligned}$$ So the coefficient matrix is $$A=\begin{pmatrix} 3&1&\beta\\ 2&\alpha&-1\\ 1&2&1 \end{pmatrix}$$ and the augmented matrix is $$\left(\begin{array}{ccc|c} 3&1&\beta&3\\ 2&\alpha&-1&-3\\ 1&2&1&4 \end{array}\right).$$ -
Since infinitely many solutions require one equation to be a linear combination of the other two, let us use the third equation to express such dependence.
Suppose in the augmented sense.
Comparing coefficients and constants:
-
Solve for using the first and fourth equations:
From the first,
Substitute into the second:
Hence
-
Now find and .
From we get
From
-
Compute the required value:
-
Therefore, the correct option is which is Option A.
-
Comparison with stored answer:
Stored correct answer = A
Our derived answer = A
So they agree.
More from Matrices and Determinants
- If the system of equations has infinitely many solutions, then is equal to :2025 · MCQ
- Let be a real matrix such that , where and are the identity and null matrices, respectively. If , where , and are real constants, then …2025 · MCQ
- Let be a matrix of order and . If , then is equal to2025 · MCQ
- Let be the identity matrix of order and for the matrix . Let be the inverse of the matrix …2025 · Numerical
- Let . If for some , then the sum of the diagonal elements of the…2025 · Numerical
- Let the matrix satisfy for . Then the sum of all the elements of is :2025 · MCQ
- Let be a matrix such that . If …2025 · MCQ
- Let the system of equations : have infinitely many solutions. Then the radius of the circle centred at and…2025 · MCQ