When going into Y= (top left button) and inserting a function into Y1 and Y2 I am not able to view them both at the same time when i select graph. (Back to the Y= screen) Next to Y1 there is a symbol that looks like a play button with a line at the end, i believe at one time this was just a slanted line. If i can get that back to the normal slanted line i think my problem would be solved... if only i knew how to do that =)

This is problem with graphing differential equation. Invalid Axes error occurs if Axes=TIME or if t(time) is set as a CUSTOM axis. This is important to noticed: if Fields=DIRFLD you cannot plot a time axis. See captured image:




This graph represented differential system of equations y1'(x)=y2(x), y2'(x)=-y1(x) for initial conditions y1(0)=0, y2(0)=-1.Finally, x axes=y1(x) and y axes=y2(x)

When you push the button [Y=] to open the function editor you will see Y1=,Y2= etc. That is the default behavior. By default the graph type is FUNCTION (y=f((x). However there are other graph types, for instance PARAM, POLAR, and SEQUENCE.
For Parametric graphs, you need two functions x as a function of t and y as a function of t. In this case, when you open the function editor, you will see pairs of functions x1(t), y1(t), x2(t), y2(t), etc. Both x and y functions of the pair must be supplied.

So if your x= function is not showing, then you must open the MODE screen, and scroll down to reach the 4th line that says FUNC, PAR, POL, SEQ. Highlight PAR and press ENTER. You do that only if you want to graph parametric functions.

In all probability, someone used the Transfrm Application before. The problem is that it lingers in memory and has to be unloaded from RAM.
To do so

1. Press the APPS button.
2. Scroll Up or down to reach the Transfrm APP.
3. Select it and press ENTER.
4. In the subsequent screen, press the number that corresponds to the UNINSTALL option.
5. Validate the selection by pressing the ENTER button.
6. Go back to your Y= Editor and enter up to 10 functions, then press the GRAPH key.
7. Graphs should know display correctly.

At some time or other you executed the Transfrm Application. I remains in ram and takes over the graphing duties from the native OS. You must unload it from memory. Do not worry this will not delete it.
To unload it from RAM

1. Press the APPS button.
2. In the list of APPS look for Transfm. You will have to scroll down or Up (faster) to get to it.
3. Select it and press [ENTER]
4. A new screen is displayed inviting you to Uninstall or Continue.
5. Press the number key corresponding to Uninstall.

Return to the [Y=] function editor to type in the functions to graph. Make sure that the = signs after the Y1,Y2, are highlighted. If one of them is not highlighted, move cursor on = and press ENTER

Let us see if I understand what you want to do. You have two functions f and g. With f and g you create four functions,

1. f+g, which you want to evaluate at 0
2. f-g, which you want to evaluate at -1
3. f*g, which you want to evaluate at 1
4. and f/g, which you want to evaluate at 3

If that is not what you intend to do, then I am sorry to I that interpreted incorrectly and you will have to post a comment with more information.
If however I did understand what you want to do, then there is a simple way to achieve this

1. In the [Y=] function editor, enter Y1 and Y2
2. In your mind decide which one represents f(x) and which represents g(x), probably f(x)=Y1(x) and g(x)= Y2(x)
   
3. Validate each one by pressing [ENTER]
   
4. Do not worry about graphing the function.
5. Press [2nd][QUIT] to return to main calculator screen
6. Enter a value (for example 5) and store it in variable X; to do so you press 5 [STO->][X,T, theta,n] [ENTER]
7. To calculate f(x)+g(x) or (f+g)(x) on the command line in main calculator screen

• Press [VARS][=>][Y-VARS][1:Function][1:Y1][ENTER]. Main calculator screen echoes Y1
• Press [+]. Screen shows Y1+
  
• Press [VARS][=>][Y-VARS][1:Function][1:Y2][ENTER]. Main calculator screen echoes Y1+Y2
• Press [ENTER] to obtain the value of f+g at X=5
  

As you can see, if you want a different operation f-g, f*g, or f`/g for a different value of X, you will have to repeat steps 6 and 7.

I am going to show you how to create a small program that will perform all the 4 operations in sequence, each time asking you for the value of X you want to use. If you are not interested, you can ignore what follows. I remain convinced that it will be helpful for other visitors.

Creating a simple program

Press [PRGM]
Use arrow to highlight [NEW]
Press [ENTER]
Screen displays
PROGRAM
Name= with alpha cursor blinking
Type in the name, for example FOPG ( meaning F operation G) or anything else. Do not use a keyword (reserved command of the TI84Plus) These are what you find in the [CATALOG].



The top line on each screen capture is inserted by the program editor after you choose the name. The last line of first screen is the the same line as the second line on 2nd screen. It must not be entered. The colon : is supplied by the program editor. It is the beginning of an instruction.

There are only to commands that are repeated here: Disp and Prompt

Disp orders the program to display

1. a message (what is between the quotation marks) or
   
2. the result of a calculation: Y1+Y2, Y1-Y2, Y1*Y2, or Y1/Y2

Prompt X will display X=? and the blinking cursor. You are supposed to enter the desired value of X and press [ENTER].
The Disp and Prompt command are accessed through the command catalog by pressing [2nd][0] (CATALOG) then scrolling along the list of commands to find the one needed. Shortcuts are possible (see below)

How to key in the program steps within the program editor
: Disp "F+G"

Press [2nd][0] (CATALOG) [X^-1](D) [Scroll Down [till...] Disp
Press [ENTER]. Editor shows :Disp
Press [ALPHA] [+] ("). Editor shows :Disp "
Press [ALPHA][COS] (F). Editor shows :Disp "F
Press [+]. Editor shows :Disp "F+
Press [ALPHA][TAN] (G). Editor shows :Disp "F+G
Press [ALPHA][+] (") Editor shows :Disp "F+G"
Press [ENTER] to validate instruction
Calculator inserts a new line :

: Disp Y1+Y2
Press [2nd][0] (CATALOG) [X^-1](D) [Scroll Down [till...] Disp
Press [ENTER]. Editor shows :Disp
Press [VARS][=>][Y-VARS][1:Function][1:Y1][ENTER]. Editor shows :Disp Y1
Press [+] . Editor shows :Disp Y1+
Press [VARS][=>][Y-VARS][1:Function][1:Y2][ENTER]. Editor shows :Disp Y1+Y2
Press {ENTER] to validate instruction
Editor inserts a new line :


:Prompt X
Press [2nd][0] (CATALOG) [8](P) [Scroll Down [till...] Prompt
Press [ENTER]. Editor shows :Prompt
Press [X,T.theta,n] key. Editor shows :Prompt X
Press [ENTER] to validate instruction
Editor inserts a new line :

To save program
Once all instructions are entered, press [2nd][QUIT] to save program.

To run program

1. Press [PRGM]
2. Under the [EXEC] menu, the list of available programs appears.
3. Type the number corresponding to the one you want to run ( FOPG) and press [ENTER].
4. The main calculator screen displays prgmFOPG and blinking cursor.
5. Press [ENTER] to make it run
6. Enter a value of X and press [ENTER]
7. Follow instructions.

Hi,
The TI84Plus has a Shade( function which allows you to represent the area you want to calculate.
The simplest syntax of the command is

Shade( lower_function, upper_function, Xleft, Xright, pattern, patern_resol) where Xleft is the left limit, Xright is the right limit, pattern is the shading pattern and pattern_resol is the resolution of the shading. Only the area where lower_function is less than upper_function is shaded. Unfortunately this command does give the value of the shaded area.

To find the area between two curves

1. Draw the curves
2. Find the left intersection point using [2nd][CALC][5:intersect]. Sorry I will not describe the procedure. The X value of the intersection point is stored in Ans memory.
3. Press [2nd][QUIT] to go to main calculator screen.
   
4. Store the Ans result in say A: [2nd][Ans][STO->][ALPHA] A
5. Return to the graph by pressing [GRAPH].
6. Find a second intersection point. Result is stored in Ans memory.
7. Press [2nd][Quit] to return to main calculator screen
8. Press [2nd][Ans][STO->][ALPHA] B to store the X value of the second intersection point in B.
9. Use the CATALOG to paste the fnInt( command to calculate the integral : [2nd][CATALOG][[APLHA] F and scroll to select fnInt( and press [ENTER]
10. To complete the command you need the identifiers Y1 and Y2.. You access the identifiers Y1 and Y2 by pressing [VARS][Y-VARS][1:Function][1:Y1] and [VARS][Y-VARS][1:Function][2:Y2]
11. The command should appear as fnInt( Y2-Y1,A,B)
12. Press [ENTER] to obtain your value.

Hope it helps.
Thank you for using FixYa.
Do not forget to rate the solution.

Hello,

Suppose you want to draw the circle the equation of which is X^2+Y^2=4, a circle centered at the origin with radius 2.
When you isolate Y^2 and then extarct the squre root you obtain two solutions, call them Y1 and Y2
Y1=SQRT(4-X^2), Y2= -SQRT(4-X^2)
You press[Y=] and type in the right hand side of the equations above, one in Y1= and the other in Y2. Press [GRAPH].

Ih a graphic does not appear within the scree window adjust the window parameters ( [WINDOW]) or Press [ZOOM] and select ZoomIn, ZoomOut, ZoomSTD, etc.

Explore the program Draw accessible by pressing [2nd][DRAW].

Hope it helps

To view both graphs, the = signs on both y1 and y2 must be contained in black boxes. If you put your cursor over the = sign on the second equation and hit enter, it turns that graph off and you won't be able to see anything but the equation in y1 line. If there is not black box around the = sign of any equation in any of the lines you have typed an equation into, you will not see the graph.

Hello,
Here how you do it taking as exemples y1=x^3 -5 and y2=abs(x^3-5)
Turn calculator ON by pressing [AC/On] . Use arrows to select [Graph] icon and press [EXE]
On line Y1= enter X[^]3 -5 [EXE]
On line Y2= press [OPTN] [F5:NUM][F1:abs] [(] X [^]3 -5 [)] [EXE]
The graphs will be drawn one after the other. You might have to adjust the window limits.
Here is an ouput drawn on another calculator.

For negative values of the x-variable, Y1 has negative values, while in the same range, Y2 has positive values, equal and opposite to those of Y1. In that range, Y1 and Y2 are symetric of each other with respect to the X axis.
For positive values of the x-variable, Y1 and Y2 are identical.

Hope it helps

Go into the Y= editor by pressing the Y= key. Select a function, then press the left-arrow a couple of times. Now press ENTER and see whether the symbol on the far left changes. If so, you've just changed the function style. Press ENTER repeatedly to select the function style. Your choices are Line, Thick, Above, Below, Path, Animate, and Dot.