Where is y2 key and +/- key

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)

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.

I think that you have the right idea. The wiring is probably wrong. If you can trace the low voltage wires to the air handler. make sure that the Y1 wire on the t-stat is going to Y1 on the hair handler and then to the condenser. The Y2 wire should be going to Y2 on the air handler and probably does not continue out to the condenser. The Y2 should be going to the contacor that brings on your backup heat. It seems like Y1 and Y2 are reversed somewhere.

This is my last post. It seems that I squanderd my time for zilch. There is a simple way to reset the defaults or the RAM. I stopped suggesting it because ..(what is the point?).
Press [2nd][MEM][7:Reset][1:All Ram][2:Yes] [ENTER]. Message RAM cleared is displayed on screen. Press [CLEAR] key. Screen should clear the message.
If that does not solve your problem..

Hello,
Sure you can. Values of Y1 and Y2 will be calculated for the same value of the independent variable. here is a screen capture taken with NO special configuration. Functions represented are Y1=2X, Y2=4X.

If you have a
Hope it helps.

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

I'm sure there are easier ways to do this but the "brute force" method is to label point A as x1, y1; point b as x2, y2 and point c as x3,y3. Then just do square root of the sum of: (x2-x1)squared+(y2-y1)squared. Save this into memory 'A'. Now do the same for x2,y2 to x3,y3 and add this to the number saved in 'A' and do it once more for x3, y3 to x1, y1 and add to the number in 'A' to get the result.

w2 and y2 are used for 2stage applications

w2 = 2 stage heat
y2= 2 stage cool

If your system is a single stage system, look for the y1 and y2 terminals. If the thermostat does not have y1 and y2 then you may have the wrong thermostat. As always, please read the directions carefully. Thanks!

I have had the same problem luckily i figured out what to do. 1. press the apps button 2. then there should be an unwanted app(it was the only one on mine) 3. pick it and hit enter 4. go to uninstall on the top of ur screen problem solved!!!! hope this helped