Difference Quotient - TI 85

This program estimates the value of a derivative at a point using the difference quotient   $f^\prime(A)\approx{f(A+H)-f(A)\over H}$
If you have not used one of the programs posted on this website before, you should read through the information in the Intro to Programming section first.

The Program
:Prompt A, H  {Prompt is in PRGM under I/O} 
:A$\to$x {The arrow is STO} {x is the x-VAR
:y1$\to$ {y1 is in VARS under EQU} 
:Disp D  {Disp is in PRGM under I/O} 

Running the Program
You will need to enter a function f(x) into y1 before running the program. To test the program try the following:
f(x)  =  x3,   A=2,   H=0.01.
The answer should be 12.0601