Texas Instruments TI-85 - Manual (Page 26)

B-26 TI-85/TI-86 Graphing Calculators
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1.4.8 PASTING A TI-85 MODEL INTO THE FUNCTION LIST The coefficients of the
model found by the calculator should not be rounded. This is not a problem because t h e
calculator will paste the entire model into the function list!
TI-85 Press MORE F4 ( STREG ) . At the Name=
prompt, type in y1 and press ENTER .
Remember that you must use a lower-case y to refer
to functions in the y(x)= graphing list.
(Any function currently in y 1 will be replaced with
the linear model.)
Press GRAPH F1 ( y(x)= ) to see the equation of
the model in the y 1 location. If you cannot see
all of the equation, press the right arrow key
to scroll the screen to the right.
1.4.9 GRAPHING A MODEL After finding a model, you should always graph it on a
scatter plot of the data to verify that the model provides a good fit to the data.
TI-85 After you have copied the model to the y(x)=
list, run program STPLT to graph the model and the
scatter plot on the same screen. The model will graph
first and then the scatter plot will appear.
TI-86 After viewing the model, be sure that Plot1 at
the top of the y(x)= list is darkened. Then, just press
EXIT F5 ( GRAPH ) to see the model and scatter plot.
1.4.10 PREDICTIONS USING A MODEL You could use one of the methods described in
Sections 1.1.7 or 1.2.1 of this Guide to evaluate the linear model at the desired input value.
Remember, if you have aligned your data, the input value at which you evaluate the model
may not be the value given in the question you are asked.
However, your calculator has a feature that gives you a very easy way to predict either
input or output values calculated from a model.
After finding a model,
TI-85 press STAT F4 ( FCST )
TI-86 press 2nd + ( STAT ) MORE F1 ( FCST )
Both Now all you need do is enter the input value x
or the output value y and press the SOLVE key to find
the value of the variable you didnÕt enter.