Question 95·Medium·Linear Equations in Two Variables
A linear function satisfies and . Which equation could represent ?
For linear-equation-from-two-points questions, immediately convert function values like into points , then compute the slope using . Use the sign of the slope to quickly eliminate any choices with the wrong slope direction (positive vs. negative), then either (1) solve for the intercept using and one point, or (2) plug one of the given -values into the remaining choices to see which one produces the correct -value. This minimizes computation and helps you answer accurately under time pressure.
Hints
Interpret the function notation
Think about what and tell you on a graph. How can you rewrite each as a coordinate pair ?
Use two points to get the slope
Once you have the two points, use the slope formula . Be careful with the negatives when subtracting.
Use slope-intercept form
After you find the slope , write and plug in one of the given points to solve for .
Compare to the answer choices
When you have an equation in the form , match both the slope and the -intercept to the given answer choices.
Desmos Guide
Plot the given points
In one expression line, type (-2, 7). In another line, type (4, -5). You should see the two points plotted on the coordinate plane.
Graph each answer choice
In separate expression lines, type each option exactly: y = -2x - 3, y = 2x + 3, y = 2x - 3, and y = -2x + 3. Four lines will appear.
Identify the correct line visually
Look at which of the four lines passes through both plotted points (-2, 7) and (4, -5). The equation of that line matches the function f and is the correct choice.
Step-by-step Explanation
Translate the function values into points
A statement like means that when , on the graph of the function.
So the information
- means the point is on the line.
- means the point is on the line.
We are looking for a line that passes through both and .
Find the slope of the line through the two points
Use the slope formula with points and :
So the slope of the line must be .
Use the slope to narrow down the choices and find the intercept
A line in slope-intercept form is .
We already found , so the equation must look like .
Now plug in one of the points, for example :
Compute , so:
Therefore, the -intercept is .
Write the final equation and match it to a choice
With slope and intercept , the line’s equation is
This matches answer choice D.