Question 31·Easy·Systems of Two Linear Equations in Two Variables
The system of linear equations is shown.
What is the solution to the system?
For systems of two linear equations where one variable has opposite coefficients (like and ), use elimination: add or subtract the equations to cancel one variable and solve quickly for the other. Then substitute that value back into either original equation to find the remaining variable. As a fast check, plug the candidate solution into both equations (or into the answer choices directly) and make sure both equations come out true before you move on.
Hints
Look for a quick way to combine the equations
Notice that the first equation has and the second has . What happens to if you add the two equations together?
Solve for one variable first
After you add the equations, you should get an equation with only . Solve that equation to find the value of .
Use substitution to find the other variable
Once you know , plug it back into either or to find .
Check each answer choice
For any answer choice you consider, plug its and into both equations and see if both equations come out true.
Desmos Guide
Rewrite each equation in y = form
Rewrite as and as so they can be graphed easily.
Graph both lines in Desmos
In Desmos, enter y = 8 - x and on a new line enter y = x - 2. Look for the point where the two lines intersect.
Read the solution from the intersection
Click or tap the intersection point of the two lines. The coordinates shown are the pair that solves the system of equations.
Step-by-step Explanation
Eliminate one variable by adding the equations
The system is
If you add the left sides and the right sides, the and terms cancel:
This simplifies to
Solve for x
From , divide both sides by :
Now you know the value of .
Substitute x back to find y
Substitute into either original equation, for example :
Subtract from both sides:
Now you know both and .
Write and check the solution as an ordered pair
The solution to the system is the ordered pair using the values you found: .
Check quickly:
- First equation: ✓
- Second equation: ✓
Since this pair makes both equations true, is the correct solution.