# Foo - Programming the quadratic formula in Ti-84?

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phantomcow2
02-15-06, 02:44 PM
I've been playing around with my graphing calculator these past few days. Of course got a few games on there, got familiar with functions. Today i got a friend to program a calculator for Specific heat. We know the formula is Specific=Change of heat/mass x change temperature

So it brings you to a menu asking if you want to find specific heat, want to find mass, etc.
And you just enter in all of the variables except what you want to figure out, and it works!

So I am feeling greedy and lazy :D
Would it be possible to make a little program for....

jschen
02-15-06, 07:08 PM
It's not particularly hard to program any of those things, but note that you probably have a built-in polynomial solver anyway. On the TI-86, it's one of the yellow functions near the top, labeled POLY. It will solve for up to 30th order polynomials, though it takes forever if you give it something that big.

By the way, I know this is unsolicited advice, but until you know an equation like the back of your hand, I discourage the habit of programming in all the equations you need. If you must, program it in to double check your work, but don't rely on it to do your work for you if you don't know how you would do it by hand. It is not true that in order to write the program, you have to understand what's going on. In order to write the program, you simply have to look at an equation and unthinkingly program it in. You just pass information from a textbook to your calculator, with no need to learn any concepts. Learning concepts is important. For example, if you understand the concept of specific heat, you can get the answers just as fast without a program, but if you don't understand it well and rely on a program, you'll get the right answer on numerical questions, but you still won't have a clue what's going on.

TexasGuy
02-15-06, 07:32 PM
a2 = b+- (
/
****
i forgot it
:(

x = (-b +- sqrt(b2-4ac))/2a
*sighs*

phantomcow2
02-15-06, 08:11 PM
well the primary reason i bought this calculator was actually because of a suggestion that somebody frm this forum gave. I found that while programming it, i learned it also. SInce i had to program for every situation, i really learned it well. I think i do much better when mathematical things are applied, so far, this has been bridging that gap

jschen
02-15-06, 08:28 PM
Yup, I remember that post recommending a graphing calculator. And graphing calculators are great things. Just make sure you're truly learning concepts, and not just putting them in short term memory (in your brain, that is) while programming. If you ever find yourself unable to explain to yourself how or why a program works, it's probably a good sign that you need to brush up on a topic. But as long as you're using it to simply speed up busywork, by all means, go for it.

In my mind, a good sign that programs are being used in place of understanding concepts is when one starts programming in things that are basically a single simple manipulation. For example, I really believe anyone who uses a specific heat-related program of the sort you described is using it as a crutch and not truly understanding concepts. Why? Because if you understand the concept, all answers are a simple multiplication or division away. And if you even take a cursory glance at the units involved, it's obvious what you're supposed to do even if you don't remember anything about specific heat. (Anything other than the right manipulation doesn't result in reasonable units.) I fail to see how running a program can be faster than simply typing in a multiplication or division. Just my opinion... feel free to disagree.

Things like the quadratic equation, on the other hand, I can understand. It's a pain to solve manually. If it weren't for the polynomial solver, why not tell the calculator how to do it and be done with it?

By the way, all that said, programming your calculator can be a useful skill. Sometimes, a brute force approach can be the most obvious way to solve something, and a calculator can check over thousands of possibilities far faster than you ever can. In math contests in high school, such an approach gave me an edge on several occasions. Take two tough problems. Pick one that you can readily solve by hand. Start thinking about it. Program a brute force method of solving the second. Run program. Solve first problem. Look to calculator screen for answer to the second problem. Repeat with the next two problems. Work about twice as fast as someone else without good calculator use skills.

phantomcow2
02-15-06, 08:34 PM
You are right in that the specific heat calculator is actually less effective with time than doing it out. One thing i notice with things like that, moles, quadratics, whatever, is that i dont really get it in class. I can follow it, but forget it almost instantly. Once i go ahead and do it myself, it "clicks". So will I be using this specific heat calculator? No, i doubt it. UNless its on the test and i want to double check answers

jschen
02-15-06, 08:42 PM
:beer: Yup, do it yourself to learn the concepts, and if that means programming a program, that's fine. I've done that myself in the past to learn a concept. (I'm a terribly lazy note-taker, so I don't write much down otherwise, and I often had trouble getting myself to do problems myself and actually learn concepts short of writing a program, which I was willing to do since it was fun.) And yes, by all means, resort to all available tools on an exam.

Now that you've had to bear with me, one trick I've kept to myself for when you reach calculus. (Or for anyone else who's bothered to read all this and is in calculus.) Your graphing calculator can handle something like 99 equations simultaneously in graphing mode. You obviously don't need that many, so you can devote many of those equations to double checking work. Here's what I used to do. y1 to y5 were for my use as I saw fit. Then with some later numbers, I would run cheater programs to double check work. I don't remember the specifics, but it was something like the following:

y11 was the 1st derivative of y1
y12 was the 2nd derivative
y13 was the 3rd derivative
y14 was the integral of y1 (from 0 to the x value)
y21 was the 1st derivative of y2
etc

So for example, if I had an answer for the second derivative of a very complex formula, I would type the formula into y1, my answer into y2, and graph y12 and y2. If the two curves perfectly match, my answer must be correct.

TexasGuy
02-15-06, 08:46 PM
*whoosh*
I wish i had the time to go back and hit math again.

phantomcow2
02-15-06, 08:48 PM
cheater programs :). I have already got plenty of those. All of those nasty formulas you suddenly are prompted to remember at teh final (which allow graphic calculators always), yea I got this program called "Algebra 2 final". Basically it has every formula you will need to know, and an example of how to use it. I call it facilitating the genuine remembering and mastery of a concept. Point slope form, standard form, parabola, its all there. Step by step directions of how to solve it, its not a program that solves it for you, just a guide to how to do it

TexasGuy
02-15-06, 08:52 PM
hehe

jschen
02-15-06, 08:54 PM
Your cheater programs are wimpy. In addition to a crib sheet, you want far more sophisticated programs. :) Where possible, don't tell me how to do it. Just solve the stupid problem for me instead. Why have a crib sheet when you can have a calculator take the test for you? :D Or at least give me a numerical answer or a plotable curve so that I can compare my answer and guarantee myself a 100% correct answer.

I never resorted to them in homework (except to check answers), but when there's something on the line, if it's not explicitly cheating, I pull all the stops. It's like racing. If something's not against the rules, and doing it is to your advantage, do it!

jschen
02-15-06, 08:58 PM
By the way, back to the quadratic formula. Did you find your polynomial solver, or do you still need a program?

phantomcow2
02-15-06, 09:01 PM

phantomcow2
02-15-06, 09:02 PM
Also worth noting, i am currently BSing an outline for an english paper, so i've not looked very hard. Plus, the main reason i want a quadratic equation solver is because I never seem to remember the damn formula!

jschen
02-15-06, 09:28 PM
Hmm, evidently, only the TI-85 and above have the polynomial solver. My dinner break's over, so I'm back to work, but if you need some help with programming in a quadratic solver, post again or PM me or something and let me know what's getting you stuck... I assume the programming language is the same as on my old TI-86, and whipping up a program like that is a piece of cake.

jschen
02-15-06, 09:35 PM
Also check out this link (http://education.ti.com/educationportal/sites/US/productDetail/us_poly_83_84.html). Evidently, there's a free download to give the TI-84 the polynomial solving and simultaneous equation solving capabilities in the TI-86.

slvoid
02-15-06, 10:37 PM
Back in my day, we only had the Ti89 and all I had to do was type solve(A*x^2+B*x+C=0,x)

jschen
02-16-06, 07:13 PM
bump...

phantomcow2, you still need a quadratic formula program? Or are you all set now?

phantomcow2
02-16-06, 07:38 PM
Nah, i think i am all set. What i would li,e but dont know if possible, is an equation solver like
X+9=5, find X.
Or X+X, 2x

jschen
02-16-06, 07:54 PM
Ah, also in the TI-85/86 and up. It's actually not too horrendously hard to program on your own, though. Just write a program to implement Newton's method to apprximate an answer. Input the left and right sides of the equation into, say, y91 and y92, have y93 set to always equal y91 - y92, input a guess for x (important when there are multiple solutions since your starting guess determines which solution you end up finding), and use the program implementing Newton's method to approximate values of x until your estimate is within a previously defined acceptable bound or until you hit a predetermined maximum number of iterations. (In certain rare cases, Newton's method will fail.)

jschen
02-16-06, 07:58 PM
Actually, never mind... it appears the TI-84 does indeed have an equation solver built in. (Basically does what I described above.) Evidently, you get to it as follows (can't verify since I use a TI-86):

1. Hit the MATH key. This takes you to the MATH menu.
2. Scroll down until the cursor is on Solver... and hit ENTER
or (for step 2)
Instead of scrolling around, you can just hit the number 0 since Solver... is option #0.

jschen
02-16-06, 08:01 PM
Also, if you need to find multiple answers, graphing the two sides of the equation separately and looking to see where they intersect is one way to estimate the answer. You can then refine the answer in the equation solver.

Alternatively, since it's hard to pick an appropriate scale for your graph sometimes, graph (left side) - (right side) and look for points where the resulting equation equals zero.