A student multiplies the first equation in a system of equations by 2 and adds the result to the second equation in the system.

Which statement describes the relationship between the solution of the initial system of equations and a solution of the equation [tex]3x + y = 7[/tex]?
[tex]\[
\begin{array}{l}
x + y = 3 \\
x - y = 1
\end{array}
\rightarrow
\begin{array}{c}
2x + 2y = 6 \\
+(x - y = 1) \\
\hline
3x + y = 7
\end{array}
\][/tex]

A. The solution of the initial system is half as great as a solution of the equation [tex]3x + y = 7[/tex].

B. The solution of the initial system is also a solution of the equation [tex]3x + y = 7[/tex].

C. The solution of the initial system is unrelated to a solution of the equation [tex]3x + y = 7[/tex].

D. The solution of the initial system is twice as great as a solution of the equation [tex]3x + y = 7[/tex].



Answer :

Let's solve the given system of equations step-by-step and determine the relationship between the solution of the initial system and the equation [tex]\(3x + y = 7\)[/tex].

### Initial System of Equations
The system of equations provided is:
[tex]\[ \begin{cases} x + y = 3 \quad \text{(1)} \\ x - y = 1 \quad \text{(2)} \end{cases} \][/tex]

### Step 1: Solving the System
First, we'll solve this system by adding the two equations to eliminate [tex]\(y\)[/tex].

1. Add equations (1) and (2):
[tex]\[ (x + y) + (x - y) = 3 + 1 \][/tex]
Simplifying the left side:
[tex]\[ x + y + x - y = 2x = 4 \][/tex]
So, we have:
[tex]\[ 2x = 4 \implies x = 2 \][/tex]

2. Substitute [tex]\(x = 2\)[/tex] back into equation (1) to find [tex]\(y\)[/tex]:
[tex]\[ 2 + y = 3 \implies y = 1 \][/tex]

### Step 2: Verify the Solution in the Second Equation
Let's verify our solution [tex]\((x, y) = (2, 1)\)[/tex] by substituting into equation (2):
[tex]\[ 2 - 1 = 1 \quad \text{which is true} \][/tex]

### Step 3: Check the Relationship with [tex]\(3x + y = 7\)[/tex]
Now, we need to determine if the solution [tex]\((2, 1)\)[/tex] also satisfies the equation [tex]\(3x + y = 7\)[/tex]:

Substitute [tex]\(x = 2\)[/tex] and [tex]\(y = 1\)[/tex] into [tex]\(3x + y\)[/tex]:
[tex]\[ 3(2) + 1 = 6 + 1 = 7 \][/tex]
This is true, meaning the solution [tex]\((2, 1)\)[/tex] satisfies the equation [tex]\(3x + y = 7\)[/tex].

### Conclusion
Given that our solution [tex]\((2, 1)\)[/tex] satisfies both the initial system of equations and the equation [tex]\(3x + y = 7\)[/tex], the correct statement is:

The solution of the initial system is also a solution of the equation [tex]\(3x + y = 7\)[/tex].

So, the answer is:
[tex]\[ \boxed{\text{The solution of the initial system is also a solution of the equation } 3x + y = 7.} \][/tex]