Texas Instruments TI-84 PLUS - Graphing Calculator Manual Book page 279

sub(
returns a string that is a subset of an existing . can be a string or a string variable.
sub( string string
is the position number of the first character of the subset. is the number of characters in
begin length
the subset.
sub(string,begin,length)
Entering a Function to Graph during Program Execution
In a program, you can enter a function to graph during program execution using these commands.
When you execute this program, enter a function to store to at the prompt.
Note: Y3 ENTRY=
Chapter 15: CATALOG, Strings, Hyperbolic Functions 272