Question 55·Easy·Linear Functions
The values of the linear function are shown in the table.
| -3 | 11 |
| -1 | 7 |
| 1 | 3 |
Which equation defines ?
For a linear function given in a table, first check how changes when changes by a fixed amount: use with any two points to get the slope. Then write the equation in slope-intercept form and substitute one pair from the table to solve for . Finally, match your equation to the choice list, or quickly test each choice by plugging in a point from the table and seeing which one matches all the values.
Hints
Look for a pattern in the table
Compare how changes as goes from to and from to . Are these changes consistent?
Use the changes to find the slope
Use with any two points from the table to find the slope of the line.
Use slope-intercept form
Once you know the slope , write the equation as and plug in one pair from the table to solve for .
Desmos Guide
Enter the table of points
In Desmos, add a table and enter the three points from the problem: , , and . You should see these three points plotted on the graph.
Graph each answer choice
In new lines, type each option as an equation in (for example, y = 2x + 5, y = -2x - 5, etc.). Desmos will draw four straight lines, one for each choice.
Compare lines to the points
Look for the line that passes exactly through all three plotted points from the table. The equation of that line is the correct choice.
Step-by-step Explanation
Find how changes as changes
Look at how changes when increases:
- From to , increases by 2 and goes from 11 to 7, which is a change of .
- From to , increases by 2 and goes from 7 to 3, which is a change of .
So for every increase of 2 in , decreases by 4.
Compute the slope of the linear function
The slope of a linear function is
Using the changes from the table:
So the slope of is , meaning the equation has the form for some constant .
Find the -intercept and write the equation
Use any point from the table, for example , and substitute into :
- Plug in and :
- Simplify: , so .
Thus the equation is , which corresponds to choice C.