Graphing the Line of Best Fit

1. Graphing the Line of Best Fit Sensei By: Gene Thompson, PHS Edited: John Boehringer, PHS

2. What to expect: • This short PowerPoint will run you through how to enter data into the calculator. • This is meant to serve as a supplement to class, and thus there is no example data included. Only the steps are shown. • Remember, it is always recommended that you write your own notes for this, rather than simply copying what is presented here!

3. Formatting • S This represents a button on the calculator. • Menus will be in bold. • Choices from a menu will have a (1) number.

4. Step 1: Enter your data Press S → 1.Edit… Enter your data in the lists provided. Typically, (x) is in the L1 list, and (y) is in the L2 list.

5. Special Note Note: If your lists are missing or out of order, you can fix this by pressing S → 5.SetupEditor and pressing enter. It will say “Done” when you finish.

6. Step 2: Linear Regression Press S → CALC → 4.LinReg(ax+b) You are now asking the calculator to match the best line to your data.

7. Step 3: Specify your lists You have to tell the calculator which lists have your x- and y-data. Press `1 for L1, , and ` 2 for L2. If your x- and y-data items are NOT in L1 and L2 respectively, use whatever list numbers they are in. You must enter a comma between the lists. This is next to the () buttons.

8. Step 4: Include Y1 This step is optional, but useful. You can ask the calculator to put your equation into ! so you don’t have to type it in. Press v → Y-VARS → 1.Function. In the next menu, choose Y1.

9. Step 5: Hit Enter Once your screen looks like the left, hit e. The calculator will give you the equation in that form. Just note that a is the slope (goes in front of x), and b is the y-intercept. Round your answer appropriately.

10. Bonus: Diagnostics If you want to turn on the diagnostics, so that you can get the correlation coefficient (the R values), press `0 to go to the catalog, and scroll down to the D’s (you can jump there by hitting i, which is the D key when a is pressed). Choose DiagnosticOn from the menu, then hit enter. When it says “Done” you have turned the R-values on.

11. Bonus: Diagnostics After doing that and running the linear regression, you will see some extra values. These aren’t necessary, but they let you know how good your data is.

12. Checking the Graph Now, if you want to see your graph, we first need to turn on the plot. Press `! to get to the first plot, and turn it on by hitting e.

13. Window Adjustments Before you can see your plot, you will have to adjust the window. Automatic option: Press Zoom 9. Do it yourself option: Press @ to bring up these options. It is best to set your x-minimum and y-minimum to zero, unless you have negative values. Set your maximums so that they reach slightly further than the biggest values in your data. The xscl stands for x-scale. It is what the marks on the axis will count by. Think of it as what you would mark on your graph if you were drawing it yourself. If you were going out to 100, you wouldn’t count by 1’s, right?

14. Finally: The graph! By pressing %, you will see your data and line. If you press !, you will notice your line’s equation was typed in by the LinReg(ax+b) function.

15. The calculator These are the buttons that we used during this demonstration, in case you were having trouble finding them. I didn’t include the numbers or 2nd Function key.