Question 100·Easy·Linear Equations in Two Variables
The table shows several values of and their corresponding values of .
| n | p |
|---|---|
| 0 | -4 |
| 1 | 2 |
| 3 | 14 |
There is a linear relationship between and . Which equation represents this relationship?
For linear-relationship table questions, quickly compute the slope using any two points (change in output over change in input), then identify the y-intercept from the row where the input is 0. Plug these into the slope-intercept form , and finally check that your equation works for all given table entries. If answer choices are given, you can also eliminate any with the wrong slope or wrong value when the input is 0 to save time.
Hints
Notice how changes when increases by 1
Compare the values of when goes from 0 to 1. How much does increase? That change is the slope, because increased by 1.
Use the point where
In a linear equation of the form , the value of when tells you . Look at the table entry for .
Form the equation from slope and intercept
Once you know the slope and the intercept , plug them into and then compare your result to the answer choices.
Check your equation against all table points
After you pick an equation, plug in , , and to see if it gives , , and . The correct equation must work for all three.
Desmos Guide
Plot the table points
In Desmos, type the three ordered pairs from the table as points: (0, -4), (1, 2), and (3, 14). You should see three points on the graph.
Graph each answer choice as a line
Enter each option as a separate line in Desmos: p = -4n + 6, p = 4n - 6, p = 6n - 4, and p = 6n + 4. Desmos will draw four lines.
See which line fits all the points
Look at the graph and find which of the four lines passes exactly through all three points from the table. The equation of that line is the correct choice.
Step-by-step Explanation
Use the table to find the slope
For a linear relationship, the slope is the change in divided by the change in .
From to :
- goes from to , so the change in is .
- The change in is .
So the slope is .
Identify the y-intercept from the table
In an equation like , the number is the value of when .
From the table, when , . So the y-intercept is .
Combine slope and intercept into slope-intercept form
A linear equation relating and can be written in the form , where is the slope and is the y-intercept.
From the earlier steps, you know:
- The slope is .
- The y-intercept is .
Now substitute these values of and into .
Write the equation and match it to a choice
Substituting and into gives
This matches answer choice C, so the correct equation is .