Question 68·Medium·Linear Functions
The linear function satisfies and .
Which equation defines ?
For linear function questions where you’re given two function values, immediately think of them as points and compute the slope using . Then, on a multiple-choice test, quickly eliminate any options with the wrong slope (wrong coefficient of ), and use one of the given points to test the remaining options; this avoids doing unnecessary algebra and reduces mistakes with signs.
Hints
Turn the function values into points
Write the information and as two coordinate points on a line. What are those points?
Think about the slope
Use the two points to calculate the slope with the formula . Is the slope positive or negative?
Use the slope to filter choices
Once you know the slope, look at the coefficient of in each option to see which ones are even possible.
Check with a point
After narrowing down the choices, substitute or into the remaining equations to see which one gives the correct function value.
Desmos Guide
Enter the four candidate lines
In Desmos, type each option as its own line:
y = 2x + 4y = -2x + 4y = -2x - 4y = 2x - 4
Plot the given points
Add the points (-3, 10) and (1, 2) in Desmos (just type them exactly like that on new lines). They will appear as points on the graph.
See which line matches both points
Look at which of the four lines passes exactly through both plotted points. The line that goes through both and corresponds to the correct equation.
Step-by-step Explanation
Interpret the information as points on a line
A linear function can be written as a line on the coordinate plane.
The statements:
mean that the graph of passes through the two points and .
Find the slope of the line through the two points
Use the slope formula with the points and :
So the slope of the line (and of the function ) is .
Use the slope to narrow down the answer choices
In a linear equation written as , the coefficient of is the slope .
Look at each option's coefficient of :
- A) has slope .
- B) has slope .
- C) has slope .
- D) has slope .
Since we found the slope must be , only choices B and C are still possible.
Test the remaining options using one of the given points
Now plug into each of the remaining choices (B and C) and see which one gives :
- Choice B:
- , which matches the given value.
- Choice C:
- , which does not match .
Therefore, the function that fits both given conditions is .