How to write a program that puts a function into Y1

Question

I looked everywhere online but I could not find the answer to this question.  I am trying to program the average value theorem into my calculator but I cant figure out how to have it prompt an equation that gets stored in Y1.  I can always just plug it in before running the program but if there is a key stroke that can make this happen I would really like to know it.

Answer 1

From the TI-83 manual,  Chapter 3-6: Defining Functions:
Defining a Function from the Home Screen or a Program

1. Press [ALPHA] ["], enter the expression, and then press [ALPHA]["] again.
2. Press [STO>].
3. Press [VARS][>]1 to select 1:Function fro the VARS Y-VARS menu.
4. Select the function name, which pastes the name to the cursor location on the home screen or program editor.

Press [ENTER] to complete the instruction.