Using Your TI-84 Plus CE Part 3: Variables, Lists, Matrices 

my calculator for the variable button it uses T is there a way to change it back to x?

Check the mode, it should be function@@emmarywalski1944

@@emmarywalski1944 USE FUNCTION

Unfortunately, the TI-84 Plus CE cannot symbolically solve equations.

+Zach Telsey Numeric variables take up very little memory, but you can delete variables from the [2nd][+] (Memory) menu.

+KermMartian thanks for the quick reply! Love the videos

+Zach Telsey Thanks! I'm hoping to get the chance to continue the series soon.

2nd, +, 7, 1, 2

Good luck! Feel free to post if you have any questions.

If you have edited them on the default screen press the store button, then 2nd+x^1 (the matrix options) and in the names tab press the variable you want to update. This will paste the variable to the default screen so that you can finally press enter.

And to follow on to GogL0L's comment, if you edited them in the Matrix Editor, you don't have to do anything - just quit the matrix editor, and they'll be saved.

You can just store a new number over it (e.g. 0->X), or you can use the Memory menu ([2nd][+][2]) to delete the variable.

Welcome to calculator programming: it's never too late to start! I bet you're storing to the X or Y variables: the Y variable in particular gets reset by displaying anything on the graphscreen, and the X variable is reset by graphing something. Try using other variables, namely anything A-W, Z, or theta. At the risk of self-promotion, I wrote a book on that topic as well (www.amazon.com/Programming-TI-83-Plus-TI-84/dp/1617290777/), and there are tons of friendly volunteers who can answer TI-BASIC questions at www.cemetech.net/forum/viewforum.php?f=19 .

Have you tried B+2->A?

Thank you!

Apologies for the slow response. The O is actually the Greek letter theta; if you switch the calculator into Polar mode (from the [MODE] menu), pressing [XTOn] produces theta instead of X. You can also get theta in any graphing mode by pressing [ALPHA][3].

You're welcome; happy to help!

Victoria: you can use the DelVar command found in the Catalog ([2nd][0]). However, you generally don't *need* to delete variables; you can just use them again and they'll be overwritten.

KermMartian Thank you!

I think no, check the comments of the previous chapter where there is a similar question and @KermMartian answers that question in a more detailed way.

I think so too! It's one of my favorites.

Thanks! Feel free to ask any followup questions you run into from your exploration with the book here or preferably on the Cemetech forum, at www.cemetech.net/forum .

You have at least two options: (1) you can store 0 to X ([0][STO>][XT0n][ENTER]), or (2) you can just overwrite X with a new value ([STO][XT0n][ENTER]). Is that what you were asking?

@@KermMartian What does ([0][STO>][XT0n][ENTER]) means? LOL sorry!! Your videos are GREAT, but please add how to undo the items you are teaching. Please!! However, I learned sooooo much from you. Great job!

@@bridgethughes9738 That sequence of keypresses will store the value 0 into the variable X, but you shouldn't need to specifically "undo" it: for example, the next time you graph something, the calculator will overwrite the value of X on its own. Thanks for the kind words; I'm glad you learned a lot!

You can go to the Solver ([MATH], go to the bottom, Solver...) and use that to solve for X in an equation of the form 0=f(X) (on older calculators) or f(X)=g(X) (on newer calculators).

That generally means that the list is empty (no elements). What were you trying to do with it?

That's correct; the built-in software can only solve an equation in the form of f(x) = g(x) (or, on the slightly older calculators, 0 = f(x)). What kind of equation are you trying to solve?

Certainly! A list is a one-dimensional ordered set of numbers, for example [1, 5, -4.239, 0]. You can use lists for many different things, such as sets of numbers collected from an experiment (individual grades on a test, heights on plants exposed to a certain amount of sunlight, number of minutes late or early trains arrived), things like coordinates (although you'd need a list of X coordinates and a list of Y coordinates), etc. Matrices, on the other hand, are two-dimensional sets of numbers, and are used for too many interesting things for me to enumerate here. If you take a look at Chapter 4 of "Using the TI-84 Plus", it explains all of this in more detail.

Sure! What error are you receiving? What value are you trying to enter?

@@KermMartian It says Error: Domain (value entered is not allowed in the function or command). We just entered some decimals for applying a chi-squared test. Can the reason be the number of decimal places (they are different, some has 3 some 4)? Thanks for the quick reply )

Number of decimal places shouldn't cause that error. A DOMAIN error generally refers to the wrong type of number in a given place, e.g. giving a decimal number instead of an integer for the matrix dimensions, or the length of a list, etc. If you're using the matrix editor directly, please make sure you're entering the values within the lower portion of the screen (i.e., not the dimensions on the top row).

@@KermMartian no no, the decimals were entered into the cells, like the 1st row and 2 column for example, not as dimensions of a matrix. I am still wondering as to why it could be an error.

Make sure you use the negative key (the one with the (-) on it), not the subtraction key.

+Catalina Vargas Valverde Unfortunately, you cannot put variables into a matrix and have them reflect the current value of that variable. For example, you can't have a matrix containing [[0 A][1 B]] and have it update every time you change the value of A and B. However, you can change the individual elements' values of (for example) matrix C like this: 2.5->[C](1,2). This sets the element at row 1, column 2 of matrix [C] to 2.5.

You generally don't need to, but if you really want to, you can do [0][STO>][XT0n] (that is, "0->X"), or go to the [2nd][+][2] (Mem Mgmt -> Delete) menu and delete it.

please answer asap, my regents exam is tomorrow and I can't have 3 saved as "x"

No ASAP needed; I tend to respond to polite questions promptly anyway. :P You don't really need to clear variables; you can just reuse them. If you really want to remove them, you can go to [2nd][+] (Mem), then 2: Mem Mgmt/Delete, then the type of variable you want to delete. Find the variable(s) you want to delete, and press [DEL].

That does not work. First, maybe I do not understand how to select the X variable; second, when I select what I think is the X variable (which appears along with other letters to have a value of 18 not 3) I get an error that says "Variable cannot be moved either to or from Archive." However, as you mentioned below, once I ran a graph of a new y= function, the value held by X changed.

It sounds like you might have archived your X variable accidentally, but perhaps graphing a new Y= function forced the calculator to unarchive X. You can manually archive and unarchive variables in the Memory menu, under [2nd][+] (Memory), [2] (Memory Management/Delete), Reals, and then press [ENTER] next to the variable you want to archive or unarchive. An asterisk next to a variable indicates that it is archived. What are you trying to do, exactly?

Like commenter Evelin I was concerned that having 3 stored in X would affect other uses of X (to be honest I am not sure why storing a value in X would ever makes sense. Perhaps if it was a long decimal that you did not want to have to enter multiple times?). In hindsight, I believe I have learned it is not a concern (proved by seeing the value change after graphing a fresh function), but my point was the instructions did not provide a path to erase the value 3 in X. BTW, no asterisks in any of the variables in the "real" section.

Joshua Treeful Depends on the Variable. REAL Vars default to zero when accessed. List and Matrix variables, however, are not so lucky - should you try to access a variable stored here that doesn't exist, you get an error message.

Can you be more specific?

@@KermMartian nevermind sorry I was just being illiterate!😂

+Texan1048 Are you on the homescreen? You can turn those menus back on from the [MODE] menu.

After you press [ALPHA][ZOOM] (F3), press the [up] arrow once, and then you'll be able to move left and right inside that menu. It's not that intuitive.

Then perhaps you should either watch the rest of these videos or read the book, so you can learn how easy it can be!

joey meyers You can't undo it, but you can store a different value to X simply by doing, say, -42 ->X. Or, you could store the value of X to a different variable before you set X, for example first doing X ->A and then 3 ->X. Then A would contain X's old value, and X would contain 3.

+KermMartian but if I then go to graph an equation such as 5X-3 it will register as 5(3)-3 right?

joey meyers Nope! When your calculator draws a graph, it actually plugs in the X coordinates of all the pixels on the screen as it graphs, overwriting whatever you had in X. If you look at X after you graph something, you'll see that it's equal to Xmax.

+KermMartian okay that makes sense thank you and I learned a lot from your videos thank you because I haven't found any better videos out there!

joey meyers I'm glad to help! I hope you'll grab a copy of "Using the TI-84 Plus" to help out with your calculator, and keep watching for future videos in this series.