There are several ways to enter a function into the TI89 graphing calculator. For basic use,
we recommend simply entering a function into the equation editor and then working with it from there.
To begin, press Y= to access the equation editor (the Y= menu). The TI89 can accommodate up to 99 functions. Simply type in the algebraic expression used to define the function. For example, to enter the quadratic function f defined by , type X ^ 2 + 3 X Ð 7 ENTER Once the function is entered, then you can perform a variety of tasks; for example, evaluate the function at a given input value, graph the function, make a table of functional values. 
