Texas Instruments TI-89 Manual Book page 17

Symbolic expressions involve variables and other symbols such
as p and ˆ. You can enter symbolic expressions into cells and
use them in formulas.
The CellSheet™ App handles variables in the following manner.
•
You can use defined and undefined variables.
•
If a variable is defined, its value will be substituted for the
variable.
•
If you use a variable in a symbolic expression and then
change the variable's value outside of the CellSheet App,
any cells using that variable will include the new value once
those cells have been recalculated.
•
You can use variables that are stored in any folder on your
unit by including the folder name with the variable name.
•
When cell names and defined variables are not part of a
formula, they are replaced by their value.
•
If a variable has the same name as a cell name, the value of
the cell will be used unless you type the folder name and
variable name, even if the variable is in the current folder.
TI-89 / TI-92 Plus / Voyage™ 200 PLT CellSheet™ App Page 17