Finding the First y-Differences of a Set of Data

x
1
3
5
7
9
11
13
y
8
6.5
5
3.5
2
0.5
-1

When the x-differences are all constant, then the y-differences (or first differences) are useful in telling if a set of data is nearly linear or not.

To find the first y-differences, press STAT, select 1:EDIT by pressing ENTER. Enter the x values in L1, and the y values in L2 as shown below.

Next, with the flashing cursor in the L3 column, press the UP ARROW once so that L3 is highlighted. Press 2nd LIST[STAT] and RIGHT ARROW to OPS menu.

 
 
 

From the OPS menu select 7: delta Listby pressing a 7. delta Listnow appears at the bottom of the screen beside L3=. Press 2nd L2[2] to type L2, and then press the ) key. Press ENTER and the y-differences will appear in the L3 column.

 
 
 

Show Me

Examining the y-differences in L3 column, we see that the data are all exactly equal to each either. This means that the data is exactly linear.



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