Question 82·Easy·Linear Functions
The linear function passes through and . Which of the following defines ?
For line-from-two-points questions, quickly compute the slope using , then either (1) plug the slope into with one point to find and write the equation, or (2) use the slope to eliminate any answer choices with the wrong and then test the remaining choices by substituting one of the given points. This keeps the work short and reduces mistakes from doing extra algebra.
Hints
Start with the slope
You are given two points on a line. What formula lets you find the slope from two points and ?
Compute the slope
Use the points and in the slope formula . Be careful with negatives in the numerator and denominator.
Use slope-intercept form
Once you know the slope , plug it and one of the points into to solve for , the -intercept.
Connect to the answer choices
After you know both and , write the equation in the form and choose the option that has the same and . You can also quickly check by plugging and into your candidate equation to see if it gives the correct -values.
Desmos Guide
Plot the given points
Type (-2,4) and (4,-2) into Desmos in separate lines. Desmos will show these as two points on the coordinate plane.
Graph all four answer choices
Enter each option as a function on its own line: y = x + 2, y = -2x + 1, y = x - 2, and y = -x + 2. Each one will appear as a different line.
Identify the matching line
Zoom or pan if needed so both points are visible. Look for the line that passes exactly through both plotted points and . The equation of that line corresponds to the correct answer choice.
Step-by-step Explanation
Understand what the function must do
A linear function that passes through and must satisfy both conditions:
Also, because it is linear, its graph is a straight line, which we can write in slope-intercept form .
Find the slope of the line
Use the slope formula with the two points and :
So the slope of the line is .
Use the slope to find the y-intercept
Now use slope-intercept form with and one of the points, for example .
Plug in , , and :
So the line has slope and -intercept .
Write the equation and match the choice
With slope and intercept , the equation of the line is
Since represents this line, , which matches choice D.