evaluating functions with ti 83 84

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TC3 → Stan Brown → TI-83/84/89 → Evaluating Functions Summary: Contents: See also: revised 5 Aug 2007 Evaluating Functions with TI-83/84 Copyright © 2001–2012 by Stan Brown, Oak Road Systems Very often, you need to evaluate a function for several values of x. Examples: ϐinding a limit or an approximation numerically, plotting on paper by plotting points. This page gives you two techniques, creating a table of values and tracing a graph. We’ll use this function to show the methods: f(x) = (x³ − 1) / (x − 1). Both Methods: Enter the Function Method 1: Table of Values Method 2: Trace on the Graph Graphing Functions on TI‐83/84 Graphing Piecewise Functions on TI‐83/84 Both Methods: Enter the Function You have to tell the TI‐83/84 what your function is, before you can use Method 1 or Method 2. If any other plots are active (highlighted), you need to turn them off. If nothing is highlighted on your Y= screen, you can skip this step. It so happens that I had Plot1 and Y2 active, as you can see below left. In the right‐hand panel I’ve deactivated both of them. Press [Y=]. Use the blue arrow keys to move the cursor onto every highlighted = sign or Plot number, and press [ENTER]. Your screen will look different, but that’s okay as long as you have nothing highlighted. 1 of 4

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Page 1: Evaluating functions with ti 83 84

TC3 → Stan Brown → TI-83/84/89 → Evaluating Functions

Summary:

Contents:

See also:

revised 5 Aug 2007

Evaluating Functions with TI-83/84

Copyright © 2001–2012 by Stan Brown, Oak Road Systems

Very often, you need to evaluate a function for several values of x. Examples: �inding a

limit or an approximation numerically, plotting on paper by plotting points. This page

gives you two techniques, creating a table of values and tracing a graph. We’ll use this

function to show the methods:

f(x) = (x³ − 1) / (x − 1).

Both Methods: Enter the Function

Method 1: Table of Values

Method 2: Trace on the Graph

Graphing Functions on TI‐83/84

Graphing Piecewise Functions on TI‐83/84

Both Methods: Enter the Function

You have to tell the TI‐83/84 what your function is, before you can use Method 1 or Method 2.

If any other plots are active

(highlighted), you need to turn them off.

If nothing is highlighted on your Y=

screen, you can skip this step.

It so happens that I had Plot1 and Y2

active, as you can see below left. In the

right‐hand panel I’ve deactivated both

of them.

Press [Y=].

Use the blue arrow keys to move the cursor onto every

highlighted = sign or Plot number, and press [ENTER]. Your

screen will look different, but that’s okay as long as you have

nothing highlighted.

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Page 2: Evaluating functions with ti 83 84

Enter the function. Cursor to any empty Y= slot.

Press [(] [x,T,θ,n] [^] [3] [−] 1 [)] [÷] [(] [x,T,θ,n] [−] 1 [)]

[ENTER].

You may be using a different function number, but make sure your entry

looks like my Y3. If you made a mistake, go back and edit it.

Method 1: Table of Values

This method works strictly by numbers.

Press [2nd WINDOW makes TBLSET].

The �irst two rows don’t matter. Press [▼] [▼] to get to the “Indpnt” row. This controls the

independent variable x.

Press [►] [ENTER] to select “Ask.”

Press [▼] [ENTER] to select “Depend: Auto.”

Your top two rows may be different, but your bottom two rows will look

like the screen at right. These settings tell the TI‐83/84 to ask you for

values of the independent variable x, then automatically calculate the

values of the dependent variable f(x).

Now you can evaluate the function at

selected x values.

Press [2nd GRAPH makes TABLE].

You may see some values on the table screen. They don’t do

any harm, but if you want you can get rid of them by hitting

[DEL] several times.

Enter the x values, one at a time. For

instance, to home in on the limit as x

approaches 1, we might enter .5, .75, .9,

.99, and so on.

Enter each x number and press [ENTER]. The TI‐83/84

immediately displays the function value.

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Page 3: Evaluating functions with ti 83 84

Method 2: Trace on the Graph

This method is a little more work, but you get a picture of the function. Start by entering the function on

the Y= screen as shown above.

Set formatting so that the desired

information will appear on your graph.

Press [2nd ZOOM makes FORMAT].

The other settings are not critical, but you need CoordOn and

ExprOn. Press the arrow keys and [ENTER] to set the modes.

Either set up the Window screen, or use

“Zoom Standard” for a �irst look at the

graph. It happens that we want the limit

as x goes to 1. Since that �its within the

standard window, we’ll use Zoom

Standard this time.

Press [ZOOM] [6] to select ZoomStd. The graph should appear

(below left).

Press [TRACE], then an x value, then [ENTER]. You should see

the function, the x value, and the y value displayed (below

right).

Enter any other values, such as .99, .995,

.999. The dot will move along the graph,

and the new y values will be displayed.

You don’t have to press [TRACE] again. Simply enter each new

x value, followed by [ENTER].

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Page 4: Evaluating functions with ti 83 84

For this function it’s not an issue, but for other functions if your x value is outside the window, you need

to press [WINDOW] and adjust Xmin or Xmax. You can only trace x values that are between Xmin and

Xmax.

This page is used in instruction at Tompkins Cortland Community College in Dryden, New York; it’s not an of�icialstatement of the College. Please visit www.tc3.edu/instruct/sbrown/ to report errors or ask to copy it.

For updates and new info, go to http://www.tc3.edu/instruct/sbrown/ti83/

4 of 4

Page 5: Evaluating functions with ti 83 84

TC3 → Stan Brown → TI-83/84/89 → Graphing Functions

Summary:

See also:

Contents:

revised 5 Aug 2007

Graphing Functions on TI-83/84

Copyright © 2001–2012 by Stan Brown, Oak Road Systems

It’s pretty easy to produce some kind of graph on the TI‐83/84 for a given function. This

page helps you with the tricks that might not be obvious. You’ll be able to "ind

asymptotes, intercepts, intersections, roots, and so on.

Evaluating Functions with TI‐83/84

Graphing Piecewise Functions on TI‐83/84

Graphing Your Function

Common Problems

Tuning Your Graph

Zooming

Adjusting the Window

Adjusting the Grid

Exploring Your Graph

Domain and Asymptotes

Function Values

Intercepts

Multiple Functions

Intersection

The techniques in this note will work with any function, but for purposes of illustration, we’ll use

Graphing Your Function

Step 1: Clear unwanted plots.

You need to look for any previously set

plots that might interfere with your

new one.

Press [Y=] (the top left button). Look at the top of the screen.

If any of Plot1 Plot2 Plot3

is highlighted, cursor to it and

press [ENTER] to deactivate it.

(No information is lost; you

can always go back and

reactivate any plot.) To verify

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Page 6: Evaluating functions with ti 83 84

that you have deactivated the

plot, cursor away from it and check that it’s not highlighted.

(Sometimes you might want to graph

more than one function on the same

axis. In this case, make sure to

deactivate all the functions you don’t

want to graph.)

Now check the lines starting with Y1=, Y2=, and so on. If any =

sign is highlighted, either delete the whole equation or

deactivate it but leave it in memory. To delete an equation,

cursor to it and press the [CLEAR] button. To deactivate it

without deleting it, cursor to its = sign and press [ENTER].

My screen looked like this

after I deactivated all old plots

and functions.

Step 2: Enter the function.

If your function is not already in y=

form, use algebra to transform it before

proceeding.

Two cautions:

For x, use the [x,T,θ,n] key,

not the [×] (times) key.

The TI‐83/84 follows the

standard order of operations.

If there are operations on top

or bottom of a fraction, you

must use parentheses — for

x+2 divided by x−3, you can’t

just enter “x+2/x−3”.

Cursor to one of the Y= lines, press [CLEAR] if necessary, and

enter the function.

Check your function and correct any

mistakes.

For example, if you see a star * in place

of an X, you accidentally used the times

key instead of [x,T,θ,n].

Use the [◄] key and overtype any mistakes.

To delete any extra characters, press [DEL].

If you need to insert characters, locate yellow INS above the

[DEL] key. Press [2nd DEL makes INS] and type the additional

characters. As soon as you use a cursor key, the TI‐83/84

goes back to overtype mode.

Step 3: Display the graph.

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“Zoom Standard” is usually a good

starting point. It selects standard

parameters of ‐10 to +10 for x and y.

Press [ZOOM] [6].

Common Problems

If you don’t see your function graph anywhere, your window is probably restricted to a region of the xy

plane the graph just doesn’t happen to go through. Depending on the function, one of these techniques

will work:

ZoomFit is a good "irst try. Press [ZOOM] [0]. (Thanks to Marilyn Webb for this suggestion.)

You can try to zoom out (like going higher to see more of the xy plane) by pressing [ZOOM] [3]

[ENTER].

Finally, you can directly adjust the window to select a speci"ic region.

For other problems, please see TI‐83/84 Troubleshooting.

Tuning Your Graph

You can make lots of adjustments to improve your view of the function graph.

Zooming

The window is your "ield of view into the xy plane, and there are two main ways to adjust it. This

section talks about zooming, which is easy and covers most situations. The next section talks about

manually adjusting the window parameters for complete "lexibility.

Here’s a summary of the zooming techniques you’re likely to use:

You’ve already met standard zoom, which is [ZOOM] [6]. It’s a good starting point for most

graphs.

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Page 8: Evaluating functions with ti 83 84

You’ve also met zoom "it, which is [ZOOM] [0]. It slides the view "ield up or down to bring the

function graph into view, and it may also stretch or shrink the graph vertically.

To zoom out, getting a larger "ield of view with less detail, press [ZOOM] [3] [ENTER]. You’ll see

the graph again, with a blinking zoom cursor. You can press [ENTER] again to zoom out even

further.

To zoom in, focusing in on a part of the graph with more detail, press [ZOOM] [2] but don’t press

[ENTER] yet. The graph redisplays with a blinking zoom cursor in the middle of the screen. Use

the arrow keys to move the zoom cursor to the part of the graph you want to focus on, and

then press [ENTER]. After the graph redisplays, you still have a blinking zoom cursor and you

can move it again and press [ENTER] for even more detail.

Your viewing window is rectangular, not square. When your x and y axes have the same

numerical settings the graph is actually stretched by 50% horizontally. If you want a plot

where the x and y axes are to the same scale, press [ZOOM] [5] for square zoom.

There are still more variations on zooming. Some long winter evening, you can read about them in the

manual.

Adjusting the Window

You may want to adjust the window parameters to see more of the graph, to focus in on just one part, or

to get more or fewer tick marks. If so, press [WINDOW].

Xmin and Xmax are the left and right edges of the window.

Xscl controls the spacing of tick marks on the x axis. For instance, Xscl=2 puts tick marks

every 2 units on the x axis. A bigger Xscl spaces the tick marks farther apart, and a smaller

Xscl places them closer together.

Ymin and Ymax are the bottom and top edges of the window.

Yscl spaces the tick marks on the y axis.

If you want to blow up a part of the graph for a more detailed view, increase Xmin or Ymin or both, or

reduce Xmax or Ymax. Then press [GRAPH].

If you want to see more of the xy plane, compressed to a smaller scale, reduce Xmin and/or Ymin, or

increase Xmax or Ymax. Then press [GRAPH].

Many of the graph windows shown in your textbook will have small numbers printed at the four edges.

If you want to make your graphing window look like the one in the textbook, press use the numbers at

left and right edges for Xmin and Xmax, the number at the bottom edge for Ymin, and the number at the

top edge for Ymax.

Adjusting the Grid

The grid is the dots over the whole window that line up to the tick marks on the axes, kind of like graph

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Page 9: Evaluating functions with ti 83 84

paper. The grid helps you see the coordinates of points on the graph.

If you see a lot of horizontal lines running across the graph, your Xscl is way too small, and the tick

marks are running together in lines. Similarly, Yscl is the number of y units between tick marks. A

bunch of vertical lines means your Yscl is too small. Press [WINDOW] and "ix either of these problems.

To turn the grid on or off: Locate yellow FORMAT above

the [ZOOM] key. Press [2nd ZOOM

makes FORMAT].

Cursor to the desired GridOn

or GridOff setting, and press

[ENTER] to lock it in.

Then press [GRAPH] to return to your graph.

Exploring Your Graph

Domain and Asymptotes

First off, just look at the shape of the graph. A vertical asymptote should

stick out like a sore thumb, such as x = 3 with this function. (Con"irm

vertical asymptotes by checking the function de"inition. Putting x = 3 in

the function de"inition makes the denominator equal zero, which tells

you that you have an asymptote.)

The domain certainly excludes any x values where there are

vertical asymptotes. But additional values may also be excluded, even if

they’re not so obvious. For instance, the graph of f(x) = (x³+1)/(x+1) looks like a simple parabola, but

the domain does not include x = −1.

Horizontal asymptotes are usually obvious. But sometimes an apparent asymptote really isn’t

one, just looks like it because your "ield of view is too small or too large. Always do some algebra work

to con"irm the asymptotes. This function seems to have y = 1 as a horizontal asymptote as x gets very

small or very large, and in fact from the function de"inition you can see that that’s true.

Function Values

While displaying your graph, press [TRACE] and then the x value you’re interested in. The TI‐83/84 will

move the cursor to that point on the graph, and will display the corresponding y value at the bottom.

The x value must be within the current viewing window. If you get the message ERR:INVALID, press

[1] for Quit. Then adjust your viewing window and try again.

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Page 10: Evaluating functions with ti 83 84

Intercepts

You can trace along the graph to "ind any intercept. The intercepts of a graph are where it crosses or

touches an axis:

x intercept where graph crosses or touches x axis because y = 0

y intercept where graph crosses or touches y axis because x = 0

Most often it’s the x intercepts you’re interested in, because the x intercepts of the graph y = f(x) are the

solutions to the equation f(x) = 0, also known as the zeroes of the function.

To "ind x intercepts: You could naïvely press [TRACE] and cursor left and right, zooming in to make a

closer approximation. But it’s much easier to make the TI‐83/84 "ind the intercept for you.

Locate an x intercept by eye. For

instance, this graph seems to have an x

intercept somewhere between x = −3

and x = −1.

Locate yellow CALC above the [TRACE] key. Press [2nd TRACE

makes CALC] [2]. (You select 2:zero because the x intercepts

are zeroes of the function.)

Enter the left and right bounds. [(-)] 3 [ENTER] [(-)] 1 [ENTER]

There’s no need to make a

guess; just press [ENTER]

again.

Two cautions with x intercepts:

Since the TI‐83/84 does approximations, you must always check the TI‐83/84 answer in the

function de"inition to make sure that y comes out exactly 0.

When you "ind x intercepts, make sure to "ind all of them. This particular function has only one

in its entire domain, but with other functions you may have to look for additional x intercepts

outside the viewing area.

Finding the y intercept is even easier: press [TRACE] 0 and read off the y

intercept.

This y intercept looks like it’s about −2/3, and by plugging x = 0 in

the function de"inition you see that the intercept is exactly −2/3.

Multiple Functions

You can plot multiple functions on the same screen. Simply press [Y=] and enter the second function

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Page 11: Evaluating functions with ti 83 84

next to Y2=. Press [GRAPH] to see the two graphs together.

To select which function to trace along, press [▲] or [▼]. The upper left corner shows which function

you’re tracing.

Intersection

When you graph multiple functions on the same set of axes, you can have the TI‐83/84 tell you where

the graphs intersect. This is equivalent to solving a system of equations graphically.

The naïve approach is to trace along one graph until it crosses the other, but again you can do

better. We’ll illustrate by "inding the intersections of y =(6/5)x−8 with the function we’ve already

graphed.

Graph both functions on the same set of

axes. Zoom out if necessary to "ind all

solutions.

Press [2nd TRACE makes CALC] [5].

You’ll be prompted First curve? If necessary, press [▲] or

[▼] to select one of the curves you’re interested in. Press

[ENTER].

You’ll be prompted Second curve? If necessary, press [▲] or

[▼] to select the other curve you’re interested in. Press

[ENTER].

Eyeball an approximate solution. For

instance, in this graph there seems to be

a solution around x = 2.

When prompted Guess?, enter

your guess. In this case, since

your guess is 2 you should

press 2 [ENTER].

Repeat for any other solutions.

As always, you should con"irm apparent solutions by substituting in both equations. The TI‐83/84 uses

a method of successive approximations, which may create an ugly decimal when in fact there’s an exact

solution as a fraction or radical.

This page is used in instruction at Tompkins Cortland Community College in Dryden, New York; it’s not an of"icialstatement of the College. Please visit www.tc3.edu/instruct/sbrown/ to report errors or ask to copy it.

For updates and new info, go to http://www.tc3.edu/instruct/sbrown/ti83/

7 of 7

Page 12: Evaluating functions with ti 83 84

TC3 → Stan Brown → TI-83/84/89 → Piecewise Functions

Summary:

See also:

revised 4 Oct 2008

Graphing Piecewise Functions on TI-83/84

Copyright © 2003–2012 by Stan Brown, Oak Road Systems

You can graph piecewise functions on your TI‐83/84 by using the TEST menu. To show

the method, we’ll graph the function

which is read “f of x equals x²+11 for x<0, 11−4x for x between 0 and 2 inclusive, and

x²−3x+5 for x>2.” This particular function, as you’ll see, doesn't have any gaps in it, but

exactly the same technique works for piecewise functions that do have gaps.

Graphing Functions on TI‐83/84

Set-up: Dot Mode

The TI‐83/84 likes to connect dots with

continuous lines or curves where it can.

But a piecewise function could have

gaps legitimately, and therefore you

want to select dot mode.

The TI‐83 and TI‐84 MODE screens are

slightly different, but the settings are

the same.

[MODE] [▼ 4 times] [►] [ENTER]

(You may need to switch between dot mode and connected mode, depending on the functions you’re

graphing, because a function with a steeply sloping graph will be hard to see in dot mode.)

Enter the Function

The general form you’re going for is

(=irst piece)(=irst condition)+(second piece)(second condition)+...

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Page 13: Evaluating functions with ti 83 84

This works because in the TI programming language a true condition is equivalent to a 1 and a false

condition to a zero. Therefore each branch of the function is turned on (multiplied by 1) in the proper

region and turned off (multiplied by 0) everywhere else.

You can have as many (piece)(condition) pairs as it takes to de=ine the function, and you always

need the parentheses around each piece and around each condition. If you have a compound condition

like 0 ≤ x ≤ 2, you can use [2nd MATH makes TEST] [►] [1] to create an and condition, or code the two

conditions inparentheses and multiply them.

For our sample function, you want to get this onto the Y= screen:

Y1=(x²+11)(x<0)+(11−4x)(0≤x and x≤2)+(x²−3x+5)(x>2)

or

Y1=(x²+11)(x<0)+(11−4x)(0≤x)(x≤2)+(x²−3x+5)(x>2)

You already know how to do all of that except the inequality signs in the tests, and as you’ll see, that’s

pretty easy.

Clear any previous plots. (Review this

on the general graphing page if you

need to.)

[Y=] and deactivate anything that’s highlighted.

Enter the =irst branch of the function

de=inition, (x²+11).

On the Y= screen, cursor to one of the Y= lines. Press [CLEAR]

if necessary, and enter the =irst piece in parentheses:

[(] [x,T,θ,n] [x²] [+] 11 [)]

Enter the test, (x<0). Press [(] [x,T,θ,n] [2nd MATH

makes TEST] [5] 0 [)]

Enter the second branch of the function

de=inition, (11−4x).

[+] [(] 11 [−] 4 [x,T,θ,n] [)]

Enter the second test, (0 ≤ x ≤ 2). You

can code this either as the product of

two tests, (0≤x)(x≤2), or with an and

condition, (0≤x and x≤2). The =irst way

saves a couple of keystrokes, so that’s

what I’ll do.

[(] 0 [2nd MATH makes TEST] [6]

[x,T,θ,n] [)] [(] [x,T,θ,n]

[2nd MATH makes TEST] [6] 2 [)]

Enter a plus sign and the last branch of

the function, (x²−3x+5).

[+] [(] [x,T,θ,n] [x²] [−] 3 [x,T,θ,n] [+] 5 [)]

Enter the last test, (x>2). [(] [x,T,θ,n] [2nd MATH makes

TEST] [3] 2 [)]

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Display the Graph

It’s often helpful to start with [ZOOM] [6], standard zoom, and then adjust the window. This particular

function, I think, is a little easier to visualize with the window parameters shown.

You can zoom, trace, and =ind values and intercepts just as you would do for any other function.

See the general graphing page for common problems.

One particular problem with piecewise functions is that the TI‐83/84 may try to connect the

pieces. Make sure you are in dot mode, not connected mode: look on the Y= screen for three dots to the

left of your equation.

What’s New

4 Oct 2008: change the function from two to three parts, to illustrate all three types of

conditions; explain how it works; explain compound conditions; add TI‐84 mode screen

26 Oct 2007: clarify TI‐83/84 keystrokes involving the [2nd] key

(various formatting improvements, suppressed)

31 Mar 2003: new document

This page is used in instruction at Tompkins Cortland Community College in Dryden, New York; it’s not an of=icialstatement of the College. Please visit www.tc3.edu/instruct/sbrown/ to report errors or ask to copy it.

For updates and new info, go to http://www.tc3.edu/instruct/sbrown/ti83/

3 of 3

Page 15: Evaluating functions with ti 83 84

TC3 → Stan Brown → TI-83/84/89 → Inverse Functions

Summary:

revised 15 Feb 2009 (What’s New?)

Inverse Functions on TI-83/84

Copyright © 2001–2012 by Stan Brown, Oak Road Systems

Graph an Inverse Function

After you graph a function on your TI‐83/84, you can make a picture of its inverse byusing the DrawInv command on the DRAW menu.

For this illustration, let’s use f(x) = √(x−2), shown at right. Though youcan easily $ind the inverse of this particular function algebraically, thetechniques on this page will work for any function.

I’ve compensated for the rectangular viewing window by settingwindow margins to 0 to 10 in the x direction and 0 to 6.5 in the ydirection. (If you don’t know how to graph a function, please review thatprocedure.)

The graph of an inverse function is a mirror image of the original through the line y=x, so I’ve havealso plotted that line.

To draw the inverse of that function:

Paste the DrawInv command to yourhome screen.

[2nd PRGM makes DRAW] Either cursor down to the 8 and press [ENTER], or simplypress [8].

Tell the TI‐83/84 to $ind the originalfunction in Y1.

Press [VARS] [►] [1] [1].(If your function was in a different numbered y variable, pickthat one instead of Y1.)

At this point your screen shows thiscommand: DrawInv Y1

Now execute the command. Press [ENTER].

The result is shown at right.

You know from your algebra work that the inverse off(x) = √(x−2)

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Page 16: Evaluating functions with ti 83 84

isf (x) = x²+2, x ≥ 0

and the graph con$irms that.

Each point on the graph of f(x) has a corresponding point on the graph of f (x). For example, f(2) = 0,so (2,0) is on the original graph, (0,2) is on the graph of f (x), and f (0) = 2.

Unfortunately, all you can do with the inverse is look at it. You can’t trace or do other things. But eventhat helps you check your work. For instance, you see that the inverse of the sample function appearsonly in the positive x region. The inverse you calculate algebraically, x²+2, has a domain in both thepositive and negative reals, but from drawing the inverse on the TI‐83/84 you can see that you need torestrict the inverse function’s domain to match the restricted range of the original function.

There’s another way you can check your work. Find the inverse function $irst, algebraically, and graph itas Y3 when you graph the original as Y1. If you do that, DrawInv Y1 will exactly overlay the graph ofyour algebraic inverse.

Caution: Because the screen resolution is low, two different functions sometimes look the same.This method isn’t an absolute guarantee that your work is correct, but it’s better than no check at all.

Find the Value of an Inverse Function

Now suppose you have to $ind f (1.5)? Of course you can look at it on the graph and estimate, but yourcalculator can do a better job of the estimation for you. There are two methods, one on the graph andone on the home screen.

Method 1: intersect on Graph

Remember that f (1.5) is some value, call it a, such that (1.5,a) is on thegraph of f (x), and therefore (a,1.5) is on the graph of f(x). In otherwords, f (1.5) is the x value on the original graph of f(x) where the yvalue is 1.5.

Using this idea, to $ind f (1.5) you can plot y = 1.5 and have yourcalculator $ind the point where it intersects the graph of f(x). You don’tneed the graph of f (x) for this at all.

The graphs are shown at right, and here’s the procedure.

Select the intersect command. [2nd TRACE makes CALC] [5]

The calculator asks “First curve?” Simply press [ENTER] to select the $irst curve.

‐1

‐1

‐1 ‐1

‐1

‐1

‐1

‐1

‐1

‐1

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Page 17: Evaluating functions with ti 83 84

The calculator then asks “Secondcurve?”

The cursor may have moved automatically to the othercurve. If not, press [▲] or [▼] until it does. Press [ENTER].

Finally, the calculator asks for yourguess.

Usually you can just press [ENTER]. But if the function is verycomplicated, you can use [◄] or [►] to move the cursor closeto the intersection point and then press [ENTER], or type in anumber and press [ENTER].

The result is shown at right: the answer is 4.25.Why is the answer x and not y? Because you’re trying to $ind f (1.5),

the value of the inverse function of 1.5. But as mentioned above, f (1.5)is the number a such that f(a) = 1.5. In other words, becausef(4.25) = 1.5, f (1.5) = 4.25.

Caution: Your calculator gives numerical solutions only. To determinewhether 4.25 is the exact answer or just a good approximation, you haveto check it in the original function.

Method 2: solve on Home Screen

You can accomplish the same thing on the home screen by using the solve function.

Select the solve function from thecatalog because it’s not in a menu.(There’s a Solver command in the Mathmenu, but setting it up is a little morework.)

Press [2nd 0 makes CATALOG] [ALPHA 4 makes T], scroll up tosolve(, and press [ENTER].

The $irst argument is an expression thatyou want to equate to zero. You actuallywant to equate Y1 to 1.5, which is thesame as equating Y1−1.5 to 0.

Press [VARS] [►] [1] [1] [−] [1] [.] [5]

The second argument is the variable, x. Press [,] [x,T,θ,n].

‐1

-1

‐1

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The last argument is your initial guess.Unless the function is prettycomplicated, it doesn’t matter what youenter here as long as it’s in the domainof the function. For example, 0 would bea bad choice for f(x) = √(x−2) becausef(0) is not a real number. Let’s use 6 asthe initial guess.

Enter the initial guess and a close parenthesis [)].

The screen is shown at right. The answer of 4.25 agrees with thegraphical method.

Caution: Again, remember that this is a numerical solution andmay not be exact.

What’s New

15 Feb 2009: Add section, suggested by Max Harwood, on $inding value of inverse function; edit thegraphing section extensively for clarity; drop “drawing” from document title

(intervening changes suppressed)

7 Jun 2003: $irst publication, as “Drawing Inverse Functions on the TI‐83”

This page is used in instruction at Tompkins Cortland Community College in Dryden, New York; it’s not an of$icialstatement of the College. Please visit www.tc3.edu/instruct/sbrown/ to report errors or ask to copy it.

For updates and new info, go to http://www.tc3.edu/instruct/sbrown/ti83/

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