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Make a TI-89 graph a circle?

I

InorganicMatter

[H]F Junkie
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Oct 19, 2004
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Seems like the best place to put it. If I'm wrong, mods please move it.

I have a standard TI-89 (not Titanium). I'm sure there is a way to make this calculator graph a circle, but I can't figure it out for the life of me. I can use the Y= editor to graph parabolas and lines, but I would like to make it graph a cirle too (and ellipses would be nice). Here is the kind of equation I am talking about:

x^2 + 2x + y^2 - 6y = 6
 
don't you have to re-arrange that equation in terms of y and then simply enter that in?

been so long since I was doing maths at school so cant quite remember...
 
Yes, but the Y= editor only lets me type in equations with a single Y, I can't find a way to let me type in a squared Y.
 
if it was an 83/84 i could help you but the 86 and 89 i have no friggin clue
 
sac_tagg said:
Yes, but the Y= editor only lets me type in equations with a single Y, I can't find a way to let me type in a squared Y.
Click to expand...
Well that's where your algebra knowledge needs to come in so you can rearrange it to be y= ....


Just had a go and couldn't do it. I could 8 years ago... :)
 
If I remember correctly if you take the sqaure root of one side of the equation that is the same as squaring the other side.

y= square root(formula)

I could be way off, its been years since I have done any sort of serious math.
 
remeber when you take square root it is +/-. So you'll need to enter one formula for plus and one for negative.
 
I'm pretty sure you aren't up to this point yet but using polar coordinate rather than rectangular make drawing circles SO much easier. At least you have something to look forward to now ;)
 
x^2+2x+y^2-6y=6

y^2-6y=6-x^2-2x

y^2-6y+9=6-x^2-2x+9=15-x^2-2x

(y-3)^2=15-x^2-2x

y-3=+/- sqrt(15-x^2-2x)

y=3 +/- sqrt(15-x^2-2x) (two equations)

I'll accept that 89 as a thank you... ;)
 
mavalpha said:
(y-3)^2=15-x^2-2x

y-3=+/- sqrt(15-x^2-2x)

y=3 +/- sqrt(15-x^2-2x) (two equations)
Click to expand...
Yeah, that's the bit I couldn't do. God, and I thought I'd never see this shit again, let alone be actually intrigued by it. Someone shoot me now!
 
no_circle.jpg


And it doesn't even form a proper circle. I feel *so* sad right now...
 
mavalpha said:
y=3 +/- sqrt(15-x^2-2x) (two equations)
Click to expand...
You can also type it as {-1,1}sqrt(15-x^2-2x)

Same thing, less typing.

If you set the "xstep" and "ystep" things (I think that's what they are) to something smaller, you'll get more of the circle.
 
Darn, too late :)

But here it is anyway:

y1=b+(sr(c-(x-a)^2)) > for top half
y2=b-(sr(c-(x-a)^2)) > bottom half

where (a,b) is the coordinates of the centre of the circle, and c is the overall size.

Mike
 
Those gaps that you see are a result of the resolution of the calculators lcd. If you zoom in on the gaps you'll see that they get smaller.
 
Not to question your reading skills (since you've already asked for help in math), but that's a TI-80- not a TI-89, unless my glasses are combining with the blurriness of the pic to produce fake text. It's a pretty big difference.
 
Wow, some people really *do* have problems with their calculators...

Hell, im using my TI 89 in math right now- i would have probably just converted that equation to a polar form, and graphed.

BTW, make sure you get Arena 3d and Phoenix for that calculator. They are great.
 
MovieMan80 said:
Those gaps that you see are a result of the resolution of the calculators lcd. If you zoom in on the gaps you'll see that they get smaller.
Click to expand...
Yes indeed they do. Crappy calculator.

mavalpha said:
Not to question your reading skills (since you've already asked for help in math), but that's a TI-80- not a TI-89, unless my glasses are combining with the blurriness of the pic to produce fake text. It's a pretty big difference.
Click to expand...
Yeah, I know, but the graphing of simple equations is the same in principle. And yeah, the pic is cWap 'cos I was just using my mobile phone.
 
Edit: Nevermind, I didn't pay attention to posters. I thought that you were the same person who started the thread. Sorry!
 
SystemERRor said:
Wow, some people really *do* have problems with their calculators...

Hell, im using my TI 89 in math right now- i would have probably just converted that equation to a polar form, and graphed.

BTW, make sure you get Arena 3d and Phoenix for that calculator. They are great.
Click to expand...

Polar form is so much eaiser and more powerful to work with especially if you're programming the formulas for your computer (or TI).

We should so a math problem of the day here, though i doubt it would fall under general hardware.
 
Rock345 said:
Polar form is so much eaiser and more powerful to work with especially if you're programming the formulas for your computer (or TI).

We should so a math problem of the day here, though i doubt it would fall under general hardware.
Click to expand...

Agree with the first, and I'm about to smack you for the second :p
 
6 years of getting your BS and MS in computer science makes math fun! Just a warning that computer science has little to do with programming and a whole lot more to do with math then you would think.
 
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