Texas Instruments TI-85 - Manual (Page 24)

B-24 TI-85/TI-86 Graphing Calculators
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output values are constant. If the first differences are ÒcloseÓ to constant, this is an
indication that a linear model may be appropriate.
Program DIFF is given in the TI-85/TI-86 Appendix.
To run the program, press PRGM F1 ( NAMES ) and
then the F -key under the name of the program. Press
ENTER . If you have not entered the data, stop the
program by pressing F2 ( Quit ) . To continue, press
F1 ( Yes ) .
At the Choice? prompt, press F1 ( 1st ) to generate
the list of first differences.
Note: You may not be able to see the complete list
on this screen. If not, go to the list editor to see the
complete list of first differences stored in
L 3 .
Exit program DIFF with F4 ( Quit ) .
TI-85 View list L 3 containing the first differences in
the output data by pressing 2nd – ( LIST ) F4 ( EDIT )
F3 ( L3 ) ENTER .
TI-86 If you do not want to use program DIFF , you can
use your TI-86 to compute first differences of any list.
Press 2nd – ( LIST ) F5 ( OPS ) MORE MORE F4
( Deltal( ) EXIT F3 ( NAMES ) and the menu key under L 2. Press
) ENTER to see the list of first differences in
the output data.
If necessary, use to scroll to the right to see the remainder of the first differences. Use
to scroll back to the left.
Be certain you have evenly-spaced input values if you are using this to give information
about first differences and linear models.
¥ Both Program DIFF should not be used for data with input ( L 1 ) values that are not evenly
spaced. First differences give no information about a possible linear fit to data with
inputs that are not the same distance apart.
1.4.7 FINDING A LINEAR MODEL Use your calculator to obtain the linear model t h a t
best fits the data. Your calculator can find two different, but equivalent, forms of the linear
model: y = ax + b or y = a + bx. For convenience, we always choose the model y = ax + b.