Question 83·Medium·Systems of Two Linear Equations in Two Variables
What ordered pair satisfies the system of equations below?
For systems of two linear equations on the SAT, elimination is usually the fastest: line up the equations, choose a variable to eliminate, multiply one (or both) equations so that variable’s coefficients become opposites, then add or subtract to get a single-variable equation. Solve for that variable, substitute back to find the other, and quickly check in both original equations. With multiple-choice answers, you can also plug each ordered pair into both equations, but elimination is often quicker and less error-prone.
Hints
Think about what a solution to a system means
You need values of and that make both equations true at the same time, not just one of them.
Choose a solving method
Decide whether elimination or substitution seems easier here. Look at the coefficients of and in both equations and think about which variable you could eliminate more quickly.
Try eliminating y
The -coefficients are and . What could you multiply one of the equations by so that the -terms become opposites and cancel when you add the equations?
Don’t forget the second variable
After you find one variable, be sure to plug it back into one of the original equations to solve for the other variable, and then check both equations.
Desmos Guide
Enter the equations
In Desmos, type 4x + y = 22 on one line and 2x - 3y = -10 on another line so both lines are graphed on the same coordinate plane.
Find the intersection point
Zoom or pan the graph until you see where the two lines cross. Click on the intersection point; Desmos will display its coordinates. Those coordinates give the ordered pair that satisfies both equations.
Step-by-step Explanation
Understand what it means to solve a system
We are given two equations in and :
We need a single ordered pair that makes both equations true at the same time, not just one of them.
Use elimination to solve for x
Elimination works by combining the equations to remove one variable.
The -terms are and . If we multiply the first equation by , the -coefficients will be and , which are opposites:
Now write this new equation together with the second original equation:
Add these equations term by term:
So , which gives .
Substitute to find y
Now substitute into either original equation to find . Using :
This simplifies to:
Subtract from both sides:
Write and verify the solution
We found and , so the ordered pair is .
Check in the second equation to be sure:
Both equations are true with , so this is the correct solution.