TI-89: Graphing Functions
(Y= ) to enter the function. If there is already an expression at \Y1=, press the
1. Use
CLEAR button It must be a function in the form y = single variable expression. y = x3. You
enter exponents using the ^ key. In our example you would press
^3
2.
Press
to see the graph. The default window is from (-10,-10) at the lower left corner to
(10,10) at the upper right corner. Lots of graphs do not fit in that window.
to change the viewing area.
3. Press
xmin : the x-coordinate of the lower left corner (default -10)
xmax: the x-coordinate of the upper right corner (default 10)
xscl: How far apart are the marked interval on the x-axis (default 1)
ymin : the y-coordinate of the lower left corner (default -10)
ymax: the y-coordinate of the upper right corner (default 10)
yscl: How far apart are the marked interval on the y-axis (default 1)
yres: relates to the resolution
You can manually change these values with this screen.
to view the zoom menu. Some of the more useful are
4. While viewing a graph, press
2: Zoom In (you have to press ENTER after you choose this one)
3: Zoom Out (you have to press ENTER after you choose this one)
6: ZStandard: Takes you back to the (-10,-10) to (10,10) window
7: ZTrig: Zooms to window appropriate to your setting of degrees vs radians (Ch 6)
9: ZData: used when you use the scatter plots – more later about this one
A: ZFit: finds some part of your graph and makes it fit the window.
(Y= ). Enter more
5. You can graph two functions on the same screen. Go back to
functions. All functions whose = sign is dark will be graphed on your screen. You can probably
change the on the left of the line Y2= to make that function appear as a darker line to compare
two graphs. Arrow till the is highlighted, and then press ENTER to cycle through the options.
To turn off a graph, move the cursor to the = sign for that function, and press Enter so the = sign is
NOT highlighted. You will not be able to tell a difference till you get the cursor off of the = sign.
You can get out of any of these screens with 2nd and ESC. (which is how you Quit)
Evaluating a Function, Method 1 using Value
Suppose you want to substitute x = -3 into the expression 3x2 - 5 x + 3
6. Use
to enter your function
Evaluating a function, Page 1 of 3
7. Enter y1=3x^2-5x+3 (remember to use the
8. Press
to view the Math menu
9. Press either ENTER or the 1 key to choose 1:value from the Math menu
10. You will see "Eval x = ?"in the bottom left of the screen.
11. Enter the number you want to substitute in for x (-3 in our example above). Be sure you use the (-)
key for negative, and not the subtract key.
12. Press ENTER
13. You will see xc=-3 in the bottom left of the screen, and yc=45 in the bottom right. That means that
your expression equals 45 when -3 is substituted in for x.
14. If you try a number outside of the viewing window, you will get an error message. You can only
test evaluate x-coordinates between Xmin and Xmax. To get outside that range, you need to
change the Window.
15. Press
to change the viewing area.
Change the xmin and/or xmax so that the numbers you want to test fit in between them. (If you
want to test 20, you could change your xmax to 25)
Evaluating a Function, Method 2 using Table
16. Press
to see a table of values. It defaults to integer steps, but you can use
change the increment.
to
17. Instead of the default ∆Tbl = 1 you can change it to ∆Tbl = 0.1 and the table will increment by 0.1
(or whatever you choose, including something like π/4)
Evaluating a Function, Method 3 using Function Notation
18. Press 2nd , ESC to go back to the “Home” screen.
19. Press the
(the
could be changed to 2 for y2(-3) and so on.
FINDING ZEROES (x-intercepts)
20. This step assumes you already have functions entered using
21. Press
to view the Math menu
22. Choose 2: Zero
Left Bound: The dialog at the bottom of the screen wants the Left Bound. Enter an x-coordinate
of a point to the left of an intercept, or move the cursor there.
ENTER
Right Bound: Enter an x-coordinate of a point to the right of an intercept, or move the cursor.
ENTER
Guess: You can just press Enter again, or you can try to speed things up by getting the cursor
closer to the x-intercept.
Evaluating a function, Page 2 of 3
ENTER
At the bottom of the screen you will see the x- and y-coordinate of the point, or it will fail if there
is none or you incorrectly chose your Left and Right Bounds.
STORING AND RETRIEVING NUMBERS
23. Suppose you want to store a complicated answer and use it later.
Find 2 + 3 to get the answer 5
Press STO
Press ALPHA
Press any key with a letter. Let’s choose “A” which is over the = button
Time goes by, and then you want to use A to evaluate 3A + 5A2
You would press:
3
ALPHA
The key for the letter you chose. (= since its alpha character is “A”)
+
5
ALPHA
The key for the letter you chose. (= since its alpha character is “A”)
^2
ENTER
Anywhere you want to use A, you do 2nd, ALPHA, =
Finding Where Two Functions Intersect
24.
25.
: Enter the two equations, one into Y1 and the other into Y2
to access the Math menu
26. Choose 5:intersect
27. The cursor is on one curve. Press ENTER.
28. The cursor is on the second curve. Press ENTER
29. Lower Bound? Move the cursor to the left of the point of intersection, and press ENTER.
30. Upper Bound? Move the cursor to the right of the point of intersection, and press ENTER.
31. The coordinates of the point of intersection are displayed at the bottom of the screen.
32. If you have more than two functions graphed, you can use the up and down arrows to select curves
in steps 33 and 34.
33. Choices 3:minimum and 4:maximum are also useful Math menu options.
If you have other brands, try the online calculator manuals.
http://www.prenhall.com/divisions/esm/app/calc_v2/ has a good site for a variety of brands.
Evaluating a function, Page 3 of 3