Question 44·Medium·Systems of Two Linear Equations in Two Variables
The solution to the system of equations
is . What is the value of ?
(Express the answer as an integer)
For systems of two linear equations, choose the method—substitution or elimination—that lets you isolate a variable with the fewest steps. If one equation has a coefficient of 1 or -1 on a variable, solve that equation for that variable and substitute into the other equation. Work carefully with negative signs, and once you find one variable, plug it back into the simpler equation to find the other. If time allows, quickly check your solution by substituting both values into both original equations.
Hints
Pick an equation to solve for one variable
Look at which equation makes it easiest to isolate or . One equation already has a term with coefficient .
Express y in terms of x
Rearrange the simpler equation so it says (something involving ). Be careful with negative signs when you move terms across the equals sign.
Substitute into the other equation
Take your expression for and plug it into the other equation. Then solve the resulting equation to find , and use that -value to get .
Desmos Guide
Graph both equations as lines
In Desmos, type 5x+3y=1 on one line and 2x-y=7 on another line. Desmos will graph both as lines in the coordinate plane.
Find the intersection point
Adjust the view (zoom or drag) until you see where the two lines cross. Tap or click on the intersection point; Desmos will show its coordinates .
Use the y-coordinate
Read the y-coordinate of the intersection point shown by Desmos. That y-value is the answer to the question.
Step-by-step Explanation
Choose a variable to isolate
Look at the system:
The second equation, , is easiest to solve for because has a coefficient of .
Solve the second equation for y
From :
- Subtract from both sides: .
- Multiply both sides by : .
Now you have written in terms of .
Substitute into the first equation and solve for x
Substitute into the first equation :
Now simplify:
So the -value of the solution is .
Find y using the value of x
Use and plug in :
Therefore, the value of is .