When working with TI-Nspire, keep in mind that variables are shared among applications within the same problem. You might want to store a variable for a variety of reasons. Here’s a list of some of those reasons:
Store a number: You may want to store a number to a variable if you expect that you’ll need to use the number in subsequent calculations. Storing a number is especially helpful if the number is irrational (or quite long) and you want to store the entire result for future use.
Define a function: The ability to define a function with a meaningful name is a powerful option. In fact, TI-Nspire has dispelled the myth that functions must have names like f(x) or g(x). Now you can create functions whose names actually tell you what the function does. Two examples are area(s) and surface_area(r,h).
Store a list: Lists can be quite long and cumbersome. By storing a list as a variable, you can recall the list using a single variable name, rather than by retyping all the elements contained in the list.
Store a matrix: Matrices can also be long and cumbersome, particularly if the matrix contains several rows and columns. Storing a matrix can save you a lot of time and effort.
In general, storing variables can be a great time-saver; it also ensures that subsequent actions that utilize stored variables are precise and accurate. Finally, there are many, many situations in which a stored variable can facilitate and enrich a mathematical exploration.
Some variables are stored automatically depending on the functions you access while using TI-Nspire. For example, each time you perform a calculation, the last answer is stored to the variable Ans. If you perform a regression on a dataset, several variables are created, such as Stat1.r (correlation coefficient), stat.resid (list of residuals), and stat1.regeqn (regression equation).
These examples also serve to remind you of the types of variables that TI-Nspire can store. The variable Stat1.r is a number. The other two variables, stat1.resid and stat1.regeqn, are a list and a function, respectively.
Variables can only be shared among pages that are part of the same problem. If you define a variable in Problem 1, this variable can be accessed only from within Problem 1. Furthermore, you can define a variable with the same name in a second problem, knowing that these two variables won’t conflict with one another.
They can take on completely separate values or meanings. You can’t create a global variable across all problems in the TI-Nspire.
A variable that is stored in a document can’t be accessed from the Scratchpad (because the Scratchpad is not part of a document to begin with).
The TI-Nspire Store Variable operator is a secondary key, accessed by pressing [CTRL][VAR]. When using this method to store a variable, follow these three steps:
Type the item, such as a value, list, matrix, or expression, you want to store on the entry line.
Press [CTRL][VAR] to open the Store command (as indicated by a small right arrow).
Type the variable name and then press [ENTER] to store the variable.
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Source:http://www.dummies.com/how-to/content/how-to-store-variables-in-the-tinspire.html
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