Question 28·Easy·Systems of Two Linear Equations in Two Variables
The ordered pair satisfies the system above. What is the value of ?
For systems of two linear equations, quickly check if adding or subtracting the equations will eliminate a variable. When one equation has and the other has , add them to cancel and get an equation in only, solve for , and (if needed) plug back into either original equation to find . On SAT questions that ask for just one variable, stop as soon as you have that variable correctly solved.
Hints
Look for a way to eliminate a variable
Compare the two equations. Is there a way to add or subtract them so that disappears?
Try adding the equations
If you add the left sides and the right sides of the two equations, what happens to and ?
Use the new equation
After cancels, you will have an equation with only . Solve that equation to find the value of .
Desmos Guide
Enter the two equations
In Desmos, type x + y = 10 on one line and x - y = 2 on another line. Desmos will graph both lines.
Find the intersection point
Look for the point where the two lines intersect. Tap or click that intersection point so Desmos shows its coordinates .
Use the x-coordinate
Read the -coordinate of the intersection point. That value is the solution for in the system.
Step-by-step Explanation
Combine the equations to eliminate
Notice that one equation has and the other has . If we add the two equations, the terms will cancel:
On the left side, and cancel, leaving:
Solve the new equation for
Now solve the simpler equation by dividing both sides by :
This gives a single value for .
State and check the value of
From the division, we get:
Quick check (optional): If , then from we get , so . Check in the second equation: , which is true. So the value of is .