Question 32·Medium·Linear Equations in Two Variables
Two linear functions are defined by
At what -value do the graphs of and intersect?
(Express the answer as an integer)
For problems asking where two linear functions intersect, immediately set the expressions equal, , because intersection means equal outputs for the same input. Then solve the resulting one-variable linear equation by moving all terms to one side and constants to the other, being careful with plus and minus signs. Finally, if time allows, substitute your -value back into both original functions to quickly confirm they produce the same -value.
Hints
Think about what intersection means
At the point where the two graphs cross, what must be true about the -values of and for the same ?
Set up an equation
Use the expressions and . If their -values are the same at the intersection, what equation can you write relating and ?
Solve the linear equation carefully
After you set equal to , combine like terms step by step: move all terms to one side and constants to the other. Be careful with the signs when you add or subtract terms.
Check your result
Once you find an -value, plug it into both and . If the -values match, you have the correct intersection -value.
Desmos Guide
Graph both functions
In Desmos, enter y = 4x - 7 on one line and y = -2x + 5 on another line so you can see both lines on the same coordinate plane.
Find the intersection point
Click or tap near where the two lines cross; Desmos will mark the intersection point. Read off the -coordinate of that intersection point—this is the -value where the graphs intersect.
Step-by-step Explanation
Use the definition of intersection
When two graphs intersect, they share a point with the same -value and the same -value. That means at the intersection point, .
So set the two expressions equal:
Collect all x-terms on one side
To solve for , first move the term to the left by adding to both sides:
which simplifies to
Now move the constant term to the right by adding to both sides:
so
Solve for x
Now divide both sides of by :
So, the graphs of and intersect at . This is the value you should enter.