Answer :
Let's solve the given system of equations using the addition method. The system of equations is:
[tex]\[ \left\{ \begin{array}{l} x + y = -3 \\ x - y = 9 \end{array} \right. \][/tex]
Step 1: Add the two equations to eliminate [tex]\( y \)[/tex]
[tex]\[ (x + y) + (x - y) = -3 + 9 \][/tex]
Simplify the left-hand side:
[tex]\[ x + x + y - y = -3 + 9 \][/tex]
Combine like terms:
[tex]\[ 2x = 6 \][/tex]
Step 2: Solve for [tex]\( x \)[/tex]
[tex]\[ 2x = 6 \implies x = \frac{6}{2} \implies x = 3 \][/tex]
Step 3: Substitute [tex]\( x = 3 \)[/tex] into one of the original equations to solve for [tex]\( y \)[/tex]
We can use the first equation [tex]\( x + y = -3 \)[/tex]:
[tex]\[ 3 + y = -3 \][/tex]
Solve for [tex]\( y \)[/tex]:
[tex]\[ y = -3 - 3 \implies y = -6 \][/tex]
Conclusion:
The solution to the system of equations is the ordered pair [tex]\( (3, -6) \)[/tex].
So, the correct choice is:
A. The solution set is [tex]\( \{ (3, -6) \} \)[/tex].
[tex]\[ \left\{ \begin{array}{l} x + y = -3 \\ x - y = 9 \end{array} \right. \][/tex]
Step 1: Add the two equations to eliminate [tex]\( y \)[/tex]
[tex]\[ (x + y) + (x - y) = -3 + 9 \][/tex]
Simplify the left-hand side:
[tex]\[ x + x + y - y = -3 + 9 \][/tex]
Combine like terms:
[tex]\[ 2x = 6 \][/tex]
Step 2: Solve for [tex]\( x \)[/tex]
[tex]\[ 2x = 6 \implies x = \frac{6}{2} \implies x = 3 \][/tex]
Step 3: Substitute [tex]\( x = 3 \)[/tex] into one of the original equations to solve for [tex]\( y \)[/tex]
We can use the first equation [tex]\( x + y = -3 \)[/tex]:
[tex]\[ 3 + y = -3 \][/tex]
Solve for [tex]\( y \)[/tex]:
[tex]\[ y = -3 - 3 \implies y = -6 \][/tex]
Conclusion:
The solution to the system of equations is the ordered pair [tex]\( (3, -6) \)[/tex].
So, the correct choice is:
A. The solution set is [tex]\( \{ (3, -6) \} \)[/tex].