Question 34·Easy·Systems of Two Linear Equations in Two Variables
A system of linear equations is given.
What is the solution to the system?
For systems of two linear equations where one variable can be easily eliminated (like and ), use elimination by adding or subtracting the equations to get a one-variable equation, solve for that variable, then substitute back into either original equation to find the other variable. Always check your final ordered pair in both equations; quickly plugging the answer choices into both equations is also an efficient backup strategy on the SAT.
Hints
Look for a way to eliminate a variable
Notice that one equation has and the other has . What happens if you add the two equations together?
Solve for one variable at a time
After you eliminate one variable, you will get a simple equation in terms of the other variable. Solve that equation first.
Substitute back and check
Once you find one variable, plug it into either original equation to find the other variable, and then make sure your ordered pair works in both equations.
Desmos Guide
Enter both equations in Desmos
Rewrite each equation in -form, then type them into Desmos as separate lines: and . This will graph two straight lines.
Find the intersection point
On the graph, locate the point where the two lines cross. Tap or click that intersection; Desmos will display its coordinates. Those coordinates give you the solution to the system.
Step-by-step Explanation
Use elimination to find
Add the two equations to eliminate :
- First equation:
- Second equation:
When you add them, the terms cancel:
Now you have a simple equation with just .
Solve for
Solve :
So the -coordinate of the solution is .
Substitute to find
Use either original equation to find . Using :
Subtract from both sides:
Multiply both sides by :
So the -coordinate of the solution is .
Write and verify the solution
The solution to the system is the ordered pair with and , so the solution is .
Quick check in both equations:
- First equation: ✓
- Second equation: ✓
Since satisfies both equations, it is the correct solution.