SOLUTION: Solve the system by substitution. 3x – y = –7 x + y = –9

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Question 81452: Solve the system by substitution.
3x – y = –7
x + y = –9

Answer by mathdoc316(9)   (Show Source): You can put this solution on YOUR website!
Step 1: Isolate one variable, using one of the equations
Step 2: Substitute that into the other equation to eliminate the variable
Step 3: Solve that resulting equation for the remaining variable
Step 4: Solve for the variable that was eliminated
Step 5: Check the solution
Step 1 will be easy here if we use the 2nd equation, , to isolate a variable. It could easily be x or y. Let's just do x since it doesn't matter that much.

Step 2: Substitute that expression for x into the first equation



Step 3: Simplify and solve for y


Add 27 to both sides

Divide both sides by -4

Step 4: Find x


Step 5: Check the solution
,


YES
YES
The solution is correct

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