Finding A Linear Function To Model Data; Using Lists Other Than L1 And L2 To Draw A Scatter Plot - Texas Instruments TI-84 Plus Manual

TI-83, TI-83 Plus, TI-84 Plus Guide
data were constant at $541, so a linear function fit the data perfectly. What information is
given by the first differences for these modified tax data?
Run program
number that is to the left of the
press
ENTER .
differences in list
These first differences are close to being constant. This information, together with the linear
pattern shown by the scatter plot, are a good indication that a linear function is likely to give a
good fit to the data.
FINDING A LINEAR FUNCTION TO MODEL DATA Throughout this course, you
will often have your calculator find a function that best fits a set of data. Your calculator can
find two different, but equivalent, forms of a linear function: y = ax + b or y = a + bx. For
convenience, we always choose the function with equation y = ax + b.
Press
2ND
press
STAT ► [CALC] 4 [LinReg(ax+b)]
calculator's "fit a linear function to the data" instruction.
Copy the fit instruction to the home
screen by pressing
time, paste the equation into the
location of the
VARS ► [Y−VARS] 1 [Function] 1
. Press
[Y1] ENTER .
CAUTION: The best-fit function found by the calculator is also called a regression function.
The coefficients of the regression function never should be rounded when you are going to use
it to make calculations, although we report our models using rounded coefficients. If you
follow the instructions given above, this is not a problem because the calculator pastes the
entire equation it finds into the
The linear equation of best fit for the modified tax data that was
entered into lists
home screen has also been copied into
this.
USING LISTS OTHER THAN L1 AND L2 TO DRAW A SCATTER PLOT: When
finding the equation of best fit, the calculator will by default use
as the output data list unless you tell it do otherwise. It is possible to use lists other than
L2
and for the input and output data. However, if you do so, you must set one of the
L2
locations to draw the scatter plot for those other lists (as described on page 19). To find
PLOT
the best-fit function, replace
function into a location other than
number corresponding to the location of the function you want. For example, these keystrokes
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by pressing
DIFF PRGM
program location and
DIFF
Press
STAT 1 [EDIT]
L3.
to return to the home screen. Then,
MODE (QUIT)
At the same
4 .
Y1
list by pressing
Y=
list at the same time the function is found.
Y=
and in Section 1.2 and displayed on the
L1 L2
and by the other lists in the fit instruction. To paste the
L1 L2
, just change
Y1
followed by the
to view the first
to access the
. Press to verify
Y1 Y=
in the instructions given above to the
Y1
as the input data list and
L1
STAT
L1
21