## Introduction: Quadratic Formula for the TI-83 and 84

Have you ever wondered if there is a way to make your calculator solve quadratic equations for you? Well, there is a fairly easy way to make your calculator do all the work for you.

Another program that I have put on Instructables is Heron's Formula.

www.instructables.com/id/Herons-Formula-program-for-the-TI-83-and-84/

## Step 1: Getting Started

You should know that a quadratic equation looks something like this: x^2-3x+2=0 or **ax^2+bx+c=0. **This will be important later on.

The first step is to press the program button on your calculator. Press the *right arrow *twice to get to new and select create new. Enter a name.

Now press *program* again and press the *right arrow* then press 2. To get letters, push the *alhpa* button. Now enter *A,B,C *and hit enter.

## Step 2: The Equation

Look at the first picture and put that on your calculator. Make sure you use the *negative* button before the first b! The -> is the store button. Press *sto-> *to get that. This just makes the equation equal to x. You may have noticed that this is only plus the square root of b squared... There is no button on this calculator for plus or minus so you will have to enter it as two separate equations.

Refer to the second picture for the second part of the equation. It is just like the first part except for a couple things.

## Step 3: Displaying Results

Press *program*, then the *right arrow*, then *3*. This will make the calculator display the answers. First open quotes (*alpha*, *+*) then put in 12 spaces (space is *alpha* then *0*) *x=* and close quotes. The equal sign is found by pressing *2nd* and then *math (test). *Then enter *,x,y* . (Hint: Press *2nd* then *alpha* to make it easier to type letters.) You can look at the picture if you need help. Make sure that you have the exact same thing as the picture below.

## Step 4: Using the Program

To exit out of this **do not hit clear!!! **This will delete everything on the line! Make sure you hit *2nd* then *mode (quit).*

Now push *program* and select the one you just made. Hit *enter* and type in the value of A. Then do this for B and C. Remember ax^2+bx+c=0. Example: x^2-3x+2=0; A=**1**, B=**-3** (use negative sign if necessary), C=**2. **The bold numbers are the numbers that you would enter in your program. After you enter all three variables hit *enter* and you get your answer.

Thanks, too lazy to work this out on my own and really didnt want to waste time solving quadratics on a test.

I've checked the program for any errors, and as far as I can tell, the programs match. However, after I select the program and press enter, I get "ERR: ARCHIVED." What could be wrong?

That means that the program is archived, which prevents it from being deleted, but also used. You need to go into memory (press 2nd, then + sign), go to option 6 (unarcharchive), then press enter. Then go to your programs, select the program you are trying to use, and press enter. Press enter again, and it will be unarchived.

I have a TI-84, followed the instructions, and added parenthesis' around the variables to ensure I got correct answers with more complicated numbers. Works great, thanks!

2x^2-x-1 isn't x=4,-2

Put 2A in parentheses

If this is not working for you try putting 2A in paretheses

Hello I am getting incorrect answers. When i type in A=1, B=3,C=-4 I get 1 and 7.5 and that's incorrect

following the script, double and triple checking, and using the test variables, my answers are x=2,-1.5

is this correct?

What were the test variables that you used? If you used A = 1, B = -3, and C=2 like I did in step 4 then you should get 2 and 1 for the answers.

What are the twelve spaces for?

It moves the X= to the right side of the screen (check out the last picture). Its not necessary, just a personal preference.

I did everything exactly like the instructions said but I get the Syntax error on my TI 84 Plus C silver edition. I made sure that all of the numbers and letters correctly and also checked the negative to make sure I was using negative sign not the minus sign.

mine did that, but it was because i'd put a comma after the C. i took it off and it was fine.

mvp

Hey there! I have been using this for a few weeks, and it has been working fine, but I just tired using it again and it is saying i have a syntax error with a parentheses, but i have not erased anything and it looks exactly how your pictures look. Do you know what the problem is?

Thanks a lot man! :)

I have enter the program as shown into a TI84 Plus Silver Edition. I have checked the program numerous times and have it entered correctly, however when I enter the negative in front of the 3 in the sample problem I get a syntax error with a quit menu or a goto menu. help

Are you sure you're using 'negative' and not 'minus'?

Strangely enough, they are two separate keys.

Could you publish the prgroam to download?

I'd been manually entering my equation for every problem and kept screwing up parentheses or +/- signs. This was exactly what I needed. Thank you, thank you, thank you!

Thank you!

If you pressed enter on accident in the end, just go back to where you pushed enter (at the spot you pressed it not after it) and press delete and youll get rid of the : marks

Very helpful

I wanted to let everyone know that I have made some changes to the program as of Feb 12, 2010. This is just a minor change but it might affect your results. Instead of having .../2A I changed it to /(2A). If you have already written the program you might want to change it. I changed the picture in step 3 accordingly.

Ok I was wondering why it would sometimes give the right answer and sometimes wouldn't. Thanks!!

Didn't work for my TI-84 Plus :/

Can you add an image of what you have? I'm guessing that you have parenthesis out of place.

Works great! This helps so much for solving Filter circuits in the S-domain. Thank you!

Just a heads up. 2A should be parenthesized, other wise it doesn't simplify the equation when the answer is irrational or complex

Thank You

For some reason, my formula is outputting incorrect results, and I believe it's when A is anything other than 1. For example, when I did 2x^2+40x+150 (x=-5 or -15,) it gives me x= -20 and -60.

Figured it out; for some reason, mine has to have parentheses around the (2A).

Hello. How does this program respond when the solution is an imaginary number(when the graph of the equation doesn't have a x-intercept). Can it display the exact solution(s) or does it just give an approximate solution in decimal notation. If it cannot display the exact solution, is there an easy way or simple alteration in the programming that can be maid to make this possible. As you can probable tell I do not actually have a calculator yet, so I can't really experiment. I will have one soon though, and it would be awesome if I could use it for this purpose. Thanks in advance for any help/time!!!

On the calculator you can go into the menu using the "mode" key and scroll down until there is a line that has an option for "REAL", "a+bi", and "re^0i". The calculator is set to "REAL" by default. All you have to do is change the setting to "a+bi" to allow the calculation of imaginary numbers. This is also handy for doing any kind of problem involving imaginary numbers.

ok. I have tried this and went back through everything...several times. one pic you show does not displays () around the 2A sto X and 2A sto Y and the next pic does, so I thought it was that. It isn't. When I am finished, I type in the 1 the -3 and the 2 and all I get is syntax error. I have checked and re checked. what am I doing wrong?

wow i just spent the past 4 months struggaling through math only to find this after i passed

hi. when you're putting in the numbers into the program, and say the equation is 12^2+x^2 =13^2 , how do we arrange it, and do we insert the power of the exponent into the program as well? thank you!

Sorry about getting back to you almost five months later... :)

I assume you are using this equation for the Pythagorean Theorem. If so, don’t use the program and just type in √(13²-12²)

If necessary write the ± symbol before your answer (*cough*5*cough*)

Hi... First i have to thanks you for posting such a awesome program onto the internet.. i followed all the instructions but i found out that the answers came out are slightly different from the correct answer. The negative and positive signs of the 2 answers have been swapped. I want to know it's my problem with my program or.. the error of the program? (i check several times)

Make sure you put the parenthesis and commas in the right spot. I might be of more help if I saw a picture or something of it.

i made same program except with the works. was the first program i made just by looking off the source on my teachers calc.

Thank you.

Your welcome!

Heh...its funny. After years of math in college and engineering classes, this has always been the first formula I've programmed into every calculator I've owned.

Thanks so much. I really appreciate it!

Good job on the guide!

You might want to display the result of (B^2-4AC) as this determines the results. if it's >0 the results are real, if it's 0 then the two results are the same and if it's < 0 the results are complex (you can display the answers by selecting "a+bi" in the [Mode] menu