Writing a TI-82 Program

Date: 02/20/98 at 21:46:25
From: George Guyer
Subject: Writing a TI-82 Program

Could you tell me where I could find out how to write a program that 
will solve quadratic equations on my TI-82 calculator? I know that I 
can download one off the Internet but I would rather write it myself. 
Can you send me the keystrokes necessary or the code as it is written? 

Thanks, 
Gig

Date: 03/01/98 at 23:30:06
From: Doctor Jen
Subject: Re: Writing a TI-82 Program

Hi there,

If I send you the code as it is written, won't that be just the same 
as if you downloaded the code off the net? You could do that, look at 
the code and see if you can work out how the program was written. 
That's often a good way to learn about programming anyway.

I have a TI-85, and I wrote a similar program not so long ago. 
I could tell you the thought processes that went into making the 
program, if you like. That would give you a guide for where to go. 
Your manual will tell you how to program your calculator to make it do 
what you want it to do (read the chapter on programming). If you 
don't have a manual or you want something a little more specific, 
try downloading the code off the net and reading it when you've got it 
(use PRGM|edit).

If we have a quadratic of the form a(x^2) + bx + c = 0, we use the 
quadratic formula to solve it, i.e.
         
     -b +- (sqrt)(b^2 - 4ac)     where (sqrt) is 'the square root of'
x = -------------------------    +- is 'plus or minus'.
             2a

You need to start up a new program, of course. PRGM|edit gives you 
a prompt; type in what you want your program to be called.

First your calculator needs to know what values you intend to use for 
a, b, c. (You can use PROMPT for this - Prompt a,b,c. This stores your 
values to a, b and c)

Then think about how you'd go about solving the equation by hand, 
using the formula. Your program will be doing this work for you, 
so you need to tell it what you would do, using the general values 
a, b and c. (You might want to take this in several steps, if you 
don't want to type it in all in one go.) Then when you run the program 
it will work out a value of x according to the formula. The formula 
says x =..., so you need to tell your calculator to give the answer it 
gets a name (store the result of the formula to X1, say, using STO> ). 

You need two solutions, one where you add (sqrt)(b^2 - 4ac) to -b, and 
one where you take it away. Tell your calculator to do both. So you'll 
eventually get two answers - maybe X1 and X2, one for the version 
where you added, one where you took it away. 

Finally, you need to tell your calculator to give you the answers it 
got. You can use Disp for this, or Outpt. Try both, see which you 
prefer.

I do hope you have a manual that can tell you how to find your way 
around in the program editor. Hope this very rough guide gave you 
an idea of how to start.

Good luck with writing your program.

-Doctor Jen,  The Math Forum
Check out our web site http://mathforum.org/dr.math/