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,
- f+g, which you want to evaluate at 0
- f-g, which you want to evaluate at -1
- f*g, which you want to evaluate at 1
- 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
- In the [Y=] function editor, enter Y1 and Y2
- In your mind decide which one represents f(x) and which represents g(x), probably f(x)=Y1(x) and g(x)= Y2(x)
- Validate each one by pressing [ENTER]
- Do not worry about graphing the function.
- Press [2nd][QUIT] to return to main calculator screen
- Enter a value (for example 5) and store it in variable X; to do so you press 5 [STO->][X,T, theta,n] [ENTER]
- 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
- a message (what is between the quotation marks) or
- 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
- Press [PRGM]
- Under the [EXEC] menu, the list of available programs appears.
- Type the number corresponding to the one you want to run ( FOPG) and press [ENTER].
- The main calculator screen displays prgmFOPG and blinking cursor.
- Press [ENTER] to make it run
- Enter a value of X and press [ENTER]
- Follow instructions.
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