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I've been trying to get the calculator to solve simultaneous equations, and it's annoyingly slow, especially with regards to the TI-89 of some of my classmates. They can get the answer in 2-3 seconds and mine will take 30-45 seconds. Some it doesn't seem to want to come anywhere close to the right answer. Is there a better solution than the MSLV to do this?

For example, 80*cos(30)-T*sin(theta)=0 and 80*cos(30)-T-T*cos(theta)=0 doesn't want to head in the right direction even with the default guesses of 0 for both variables. I assigned units of degrees to the numbers so they would work right. I figured it would whip it out in no time, but it kept going so I interrupted it and just plugged it in by hand. That's a relatively simple one to do that way, but they aren't all so simple.

I'm somewhat new to the calculator and have only scratched the surface of what it can do, so maybe I'm going about this all wrong. I would love to hear that because it's embarrassing to still be waiting while the TI crowd has long since had the answer. Also frustrating thinking ahead to exams when I might not have the extra time to wait. (No, I'm not worried about the 45 seconds, but the few different sets of equations that I had to interrupt because they weren't even headed the right way.)

I've done a bunch of google searches, I've downloaded different solvers, but I can't seem to get them to work like they should. I get them installed, but then using them is usually not as easy as I expect and it seems like I'm fighting them MUCH more than they're helping me. If there's one I should definitely try out, please let me know.

Thanks in advance!!

Erik

For: 80*cos(30)-T*sin(theta)=0 and 80*cos(30)-T-T*cos(theta)=0
and default guesses of 0 for both variables.

T = 12.34 and theta = 1.57

time = 5 seconds

With default guesses of 1 for both variables
theta = 7.85 [1.57+2*Pi]

Regards,
Damir

Edited: 2 Oct 2008, 11:28 a.m.

Well, the time that it took is great, but the answers are wrong. Did you put the 30 degrees in as radians? I'm sorry if I didn't make it clear that they were degrees. That's the only reason I can think of why it would give back faulty answers, other than it's not programmed well. But if you regularly use it and like it then it would surprise me if it wasn't a quality program.

Should be T=46.2 and theta = 60 degrees, or 1.047rad.

You can verify that by doing it by hand, solving the first equation and then putting that number into the bottom one to solve for T.

(Although to convert from rad to deg it should be (number in rad)*180/pi not addition.)

Either way I will download and try out that solver since it is quick and see if I can make it work for me.

Edit: Funny that this is also one I've already tried out, but couldn't get it to work. (One problem was that I was trying so many of them at a time that I got overwhelmed and lost track of which was which and then got frustrated.)

Thank you! I really appreciate the response!

Erik

Edited: 2 Oct 2008, 11:49 a.m.

Quote:
Well, the time that it took is great, but the answers are wrong. Did you put the 30 degrees in as radians? I'm sorry if I didn't make it clear that they were degrees. That's the only reason I can think of why it would give back faulty answers, other than it's not programmed well. But if you regularly use it and like it then it would surprise me if it wasn't a quality program.

Should be T=46.2 and theta = 60 degrees, or 1.047rad.

You can verify that by doing it by hand, solving the first equation and then putting that number into the bottom one to solve for T.

(Although to convert from rad to deg it should be (number in rad)*180/pi not addition.)

Either way I will download and try out that solver since it is quick and see if I can make it work for me.

Edit: Funny that this is also one I've already tried out, but couldn't get it to work. (One problem was that I was trying so many of them at a time that I got overwhelmed and lost track of which was which and then got frustrated.)

Thank you! I really appreciate the response!

Erik

Yes,I put the calculator in radians mode.
Sorry.
If I put calc in degrees mode and initial guesses are 0,
solvesys gives
T=69.2820322326 and
theta=90.0000000246.

I use that numbers in first and second equation
and it gives 0.

Regards,
Damir

Edited: 2 Oct 2008, 3:50 p.m.

I EVALuated the COS(30) in DEGrees mode Exact on (getting \v/3/2)
and using initial guesses of [46.2 1.047] got in RADians mode Approx. on:
[69.2820323028 1.57079632679]
in 39.9 seconds using MSLV
(which using XQ to the Theta item produced 1/2*\pi)

Better to load SolveSys library

I finally figured out why nothing is working out quite right - it was late last night when I was posting, and I didn't give you the correct formula. The first cosine is actually supposed to be sine.

Here's the correct formula:

80*sin(30)-T*sin(theta)=0 and 80*cos(30)-T-T*cos(theta)=0

Sorry about that. That will of course affect the calculations just a tiny bit... :)

That program at the same link will do it quickly, and even stay in degrees mode? (Kind of a rhetorical question, since I'm going to go download it right now and play with it so I will find the answer out very soon.)

Thank you!
Erik

Quote:
(getting \v/3/2)

I'm sorry, but I don't understand the shorthand or conventions behind this notation. What does that mean?

Quote:
which using XQ to the Theta item

I never had heard of XQ before, but I looked it up in CAT and checked the help on it - it's very useful! That's a wonderful little thing to know, thank you!

Erik

Quote:

That program at the same link will do it quickly, and even stay in degrees mode? (Kind of a rhetorical question, since I'm going to go download it right now and play with it so I will find the answer out very soon.)

Thank you!
Erik

Yes!
And at late night hours you should drink some coffee :)

Regards,
Damir

Edited: 2 Oct 2008, 5:29 p.m.

http://hpconnect.sourceforge.net/trigraphs.html

Using your 46.2 1.047 and RADians mode
after simplifying the formula to
V=Square Root O=Theta

['40-T*SIN(O)' '40*V3-T*(1/COS(O))']
['T' 'O']
[46.2 1.047]

{MSLV}HEAD MEM;TEVAL
gave
[46.1880215352 2.09439510239]
in 19 seconds
using XQ to the 2nd item gave
2/3*pi

If the gusses are far from these
I don't know how much time it will take

with the unsimplified equations and in DEGrees mode
SolveSys gives the answer almost immediately
using maximum tolerances selected
46.2 and 60. giving
46.1880215352 and 120.
BUT
with bad guesses I'm not willing to wait

You need the TI-89 for this kind of problem solving

I tried SolveSys with RADians mode and simplified equatuations
tolerances set to max and guesses RESET to 1. 1.
and the answer was quickly
T=46.1880215352 O=-4.1887902047
the latter processed with XQ gave -4/3*pi
or with R->D -240.

So you don't need TI after all, SolveSys is enough
but I think it's good to have BOTH calcs