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Use elimination to solve the system of equations.

[tex]
\begin{array}{l}
3x + 2y = 7 \\
-9x - 6y = -21
\end{array}
[/tex]

A. The solution is [tex]$(3, -1)$[/tex].
B. There are infinitely many solutions.
C. There are no solutions.
D. The solution is [tex]$(1, 2)$[/tex].

Sagot :

Let's solve the given system of equations using the elimination method step-by-step.

We are given the system of equations:
[tex]\[ \begin{array}{l} 3x + 2y = 7 \quad \text{(Equation 1)} \\ -9x - 6y = -21 \quad \text{(Equation 2)} \end{array} \][/tex]

### Step 1: Align the Coefficients

To eliminate one of the variables, we first align the coefficients of either [tex]\(x\)[/tex] or [tex]\(y\)[/tex]. Here, we notice that multiplying Equation 1 by 3 will align the coefficients of [tex]\(x\)[/tex]:

[tex]\[ 3 \times (3x + 2y) = 3 \times 7 \][/tex]
[tex]\[ 9x + 6y = 21 \quad \text{(New Equation 1)} \][/tex]

Equation 2 remains the same:
[tex]\[ -9x - 6y = -21 \quad \text{(Equation 2)} \][/tex]

### Step 2: Add the Equations

Next, we add the New Equation 1 and Equation 2 to eliminate [tex]\(x\)[/tex]:

[tex]\[ (9x + 6y) + (-9x - 6y) = 21 + (-21) \][/tex]

This simplifies to:
[tex]\[ 0x + 0y = 0 \][/tex]
[tex]\[ 0 = 0 \][/tex]

### Step 3: Analyze the Result

The result of [tex]\(0 = 0\)[/tex] is always true. This indicates that the two original equations are actually the same line when simplified proportionally, meaning they overlap entirely.

### Conclusion

Since the equations represent the same line, there are infinitely many solutions. In other words, every point on the line defined by [tex]\(3x + 2y = 7\)[/tex] will satisfy both equations.

Thus, the solution to the system of equations is:
```
There are infinitely many solutions.
```
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