$-3 < k < 3$
$k \neq 0$
To determine the condition for the system of linear equations to have a unique solution, we need to ensure that the coefficient matrix has a non-zero determinant. The given system of equations is:
x + y + z = 2
2x + y - z = 3
3x + 2y + kz = 4
The corresponding coefficient matrix is:
1 | 1 | 1 |
2 | 1 | -1 |
3 | 2 | k |
We calculate the determinant of this matrix. The determinant, Δ, is calculated as follows for a 3x3 matrix [A]:
Δ = a(ei − fh) − b(di − fg) + c(dh − eg)
Applying this to our matrix, we calculate:
Δ = 1((1)(k) - (-1)(2)) - 1((2)(k) - (-1)(3)) + 1((2)(2) - (1)(3))
Δ = (1)(k + 2) - (1)(2k + 3) + (1)(4 - 3)
Δ = k + 2 - 2k - 3 + 1
Δ = k + 2 - 2k - 3 + 1
Δ = -k
For the system to have a unique solution, we need the determinant to be non-zero:
-k ≠ 0
This implies k ≠ 0.
Thus, the correct answer is: k ≠ 0.
To determine when the system has a unique solution, the determinant of the coefficient matrix must be nonzero. The coefficient matrix for the system is:
\[A=\begin{bmatrix} 1 & 1 & 1 \\ 2 & 1 & -1 \\ 3 & 2 & k \end{bmatrix}\]
The determinant of A is:
\[\det(A)=\begin{vmatrix} 1 & 1 & 1 \\ 2 & 1 & -1 \\ 3 & 2 & k \end{vmatrix}\]
Expanding along the first row:
\[\det(A)=1 \cdot \begin{vmatrix} 1 & -1 \\ 2 & k \end{vmatrix} - 1 \cdot \begin{vmatrix} 2 & -1 \\ 3 & k \end{vmatrix} + 1 \cdot \begin{vmatrix} 2 & 1 \\ 3 & 2 \end{vmatrix}\]
Calculate each minor:
\[\begin{vmatrix} 1 & -1 \\ 2 & k \end{vmatrix} = (1)(k) - (2)(-1) = k + 2\]
\[\begin{vmatrix} 2 & -1 \\ 3 & k \end{vmatrix} = (2)(k) - (3)(-1) = 2k + 3,\]
\[\begin{vmatrix} 2 & 1 \\ 3 & 2 \end{vmatrix} = (2)(2) - (3)(1) = 4 - 3 = 1.\]
Substitute these values back:
\[\det(A) = 1(k + 2) - 1(2k + 3) + 1(1).\]
Simplify:
\[\det(A) = k + 2 - 2k - 3 + 1 = -k.\]
For the system to have a unique solution, \(\det(A) \neq 0\). Thus:
\[-k \neq 0 \implies k \neq 0.\]
Final Answer:
\[k \neq 0.\]
A person wants to invest at least ₹20,000 in plan A and ₹30,000 in plan B. The return rates are 9% and 10% respectively. He wants the total investment to be ₹80,000 and investment in A should not exceed investment in B. Which of the following is the correct LPP model (maximize return $ Z $)?