Question 102·Hard·Systems of Two Linear Equations in Two Variables
The ordered pair satisfies the system of equations above. What is the value of ?
(Express the answer as an integer)
For systems that include parentheses, first simplify each equation by distributing and combining like terms so you have a clean pair of linear equations in standard form. Then choose elimination or substitution—elimination is usually fastest on the SAT when coefficients are not too large—multiply equations as needed to cancel one variable, solve for the other, and back-substitute. Finally, pay close attention to what the question actually asks for (such as or ) and compute that quantity from your solutions rather than stopping at the individual variable values.
Hints
Simplify the equations first
Before trying to solve the system, distribute the numbers outside the parentheses in each equation and combine like terms so each equation looks like .
Work with the simplified system
After distributing, you should get a simpler system in and . Think about using elimination (or substitution) to solve the two linear equations.
Choose a variable to eliminate
Look at the coefficients of and in the simplified equations. Which variable can you eliminate more easily by multiplying the equations and adding or subtracting them?
Answer what the question asks for
Once you find and , remember the question asks for , not just or just . Add the two values carefully.
Desmos Guide
Enter the first equation
In Desmos, type the first equation exactly as given: 2(7x-5y)-(4x+3y)=59. Desmos will graph this relation as a line.
Enter the second equation
On a new line, type the second equation: 3(4x+3y)+(7x-5y)=26. This will graph the second line.
Find the intersection point
Adjust the viewing window if needed so both lines are visible. Click on their point of intersection; Desmos will display the coordinates of that point.
Compute x + y from the intersection
Take the -coordinate and -coordinate of the intersection point you found in Desmos and add them together to get the value of .
Step-by-step Explanation
Distribute and simplify both equations
First, remove the parentheses by distributing.
For the first equation:
Combine like terms:
So the first equation becomes:
For the second equation:
Combine like terms:
So the second equation becomes:
Now the simplified system is:
Use elimination to solve for x
Eliminate by making the -coefficients opposites.
Multiply the first equation by and the second equation by so that the -terms become and :
- First equation :
- Second equation :
Now add these two new equations:
The -terms cancel:
Solve for by dividing both sides by :
Substitute to find y
Substitute into either simplified equation. Using :
So:
Subtract from both sides:
Divide by :
Compute x + y
Now that and , add them to find :
So the value of is .