Texas Instruments TI-85 User Manual

Page 26

B-26

TI-85/TI-86 Graphing Calculators

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

(

STREG

) . At the

Name=

prompt, type in

and press

ENTER

Remember that you must use a lower-case

to refer

to functions in the

y(x)=

graphing list.

(Any function currently in

will be replaced with

the linear model.)

Press

GRAPH

(

y(x)=

) to see the equation of

the model in the

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

the top of the

y(x)=

list is darkened. Then, just press

EXIT

(

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

(

FCST

)

TI-86

press

2nd

(

STAT

)

(

FCST

)

Both

Now all you need do is enter the input value

or the output value

and press the

SOLVE

key to find

the value of the variable you didnÕt enter.