How many solutions does this system have?

[tex]\[
\begin{cases}
2x + y = -2 \\
x + y = -1
\end{cases}
\][/tex]

A. One
B. None
C. Infinite



Answer :

To determine the number of solutions for the given system of equations:
[tex]\[ \left\{\begin{array}{r} 2x + y = -2 \\ x + y = -1 \end{array}\right. \][/tex]
we can proceed as follows:

1. Write down the system of equations:
[tex]\[ \begin{cases} 2x + y = -2 \quad \text{(1)} \\ x + y = -1 \quad \text{(2)} \end{cases} \][/tex]

2. Represent the system in matrix form [tex]\( \mathbf{A} \mathbf{x} = \mathbf{b} \)[/tex]:
[tex]\[ \mathbf{A} = \begin{pmatrix} 2 & 1 \\ 1 & 1 \end{pmatrix}, \quad \mathbf{x} = \begin{pmatrix} x \\ y \end{pmatrix}, \quad \mathbf{b} = \begin{pmatrix} -2 \\ -1 \end{pmatrix} \][/tex]

3. Calculate the determinant of the coefficient matrix [tex]\( \mathbf{A} \)[/tex]:
The determinant [tex]\( \Delta \)[/tex] of matrix [tex]\( \mathbf{A} \)[/tex] can be determined as follows:
[tex]\[ \Delta = \begin{vmatrix} 2 & 1 \\ 1 & 1 \end{vmatrix} = (2 \cdot 1) - (1 \cdot 1) = 2 - 1 = 1 \][/tex]

4. Analyze the determinant:
Since the determinant [tex]\( \Delta \)[/tex] is [tex]\( 1 \)[/tex], which is non-zero, it implies that the coefficient matrix [tex]\( \mathbf{A} \)[/tex] is invertible. This means the system of equations has a unique solution.

By this analysis, we conclude that the given system of linear equations has exactly one solution.

Thus, the correct answer is:

- One