3 ways to solve a system of equations [Archive]

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Stork

06-20-2005, 10:40 PM

2x + 3y +5z = 1
3x +y -z = 2
-2x +2y -8z = 5

I need 3 ways to solve this, if you can do this before I get around to it you'll make my life just a little bit easier.

RocketManJames

06-20-2005, 10:49 PM

1) Solve it manually using substitution.
2) Cramer's Rule
3) Matrix Inversion

and here are some freebies...

4) Graph them all and find the 3-way intersections
5) Trial and Error (might take a long ass time though)

-RMJ

Stork

06-20-2005, 11:00 PM

Thanks.

Cramers rule is using determinants correct?

Bah I messed up somewhere. Using substitution I got x= -19/11, but using matrix inversion I got x = -.0849...

wmspringer

06-21-2005, 12:05 AM

Yup, Cramer's rule is matrices (x=Dx/D)

If I was solving it three different ways I'd do:
1) substitution
2) elimination
3) Cramer's rule
.
.
.
4) Matlab /images/graemlins/grin.gif

vulturesrow

06-21-2005, 04:10 AM

[ QUOTE ]
4) Matlab

[/ QUOTE ]

This is actually choice #1 for we liberal arts majors (I was Econ) who were forced to take technical courses. /images/graemlins/grin.gif

Victor

06-21-2005, 04:45 AM

[ QUOTE ]
[ QUOTE ]
4) Matlab

[/ QUOTE ]

This is actually choice #1 for we liberal arts majors (I was Econ) who were forced to take technical courses. /images/graemlins/grin.gif

[/ QUOTE ]

as an engineer i am impressed if you actually learned matlab.

Frequitude

06-21-2005, 09:41 AM

[ QUOTE ]
2x + 3y +5z = 1
3x +y -z = 2
-2x +2y -8z = 5

I need 3 ways to solve this, if you can do this before I get around to it you'll make my life just a little bit easier.

[/ QUOTE ]

All I do at work is play with Matlab and read 2+2, so I gotta reply...Throwing your numbers into Matlab using

rref([[2 3 5 1];[3 1 -1 2];[-2 2 -8 5]])

gives:
x 0.20754716981132
y 0.93396226415094
z -0.44339622641509

I see that neither of your answers above for x are right, so just helping a brother out.

Cheers.

Edit: now if only someone can help me out with my Matlab problem post...

Maulik

06-21-2005, 10:49 AM

[ QUOTE ]
Yup, Cramer's rule is matrices (x=Dx/D)

If I was solving it three different ways I'd do:
1) substitution
2) elimination
3) Cramer's rule
.
.
.
4) Matlab /images/graemlins/grin.gif

[/ QUOTE ]

I don't follow?

evans075

06-21-2005, 11:35 AM

edtost

06-21-2005, 11:42 AM

Patrick del Poker Grande

06-21-2005, 12:13 PM

[ QUOTE ]
...and disappointed that you didn't use mathematica instead.

[/ QUOTE ]
Oh my aching ass. Not to go all uber-nerd on everybody here, but this is just a stupid, stupid comment.

hobbsmann

06-21-2005, 12:18 PM

[ QUOTE ]
[ QUOTE ]
...and disappointed that you didn't use mathematica instead.

[/ QUOTE ]
Oh my aching ass. Not to go all uber-nerd on everybody here, but this is just a stupid, stupid comment.

[/ QUOTE ]
Whats wrong with Mathematica?

Patrick del Poker Grande

06-21-2005, 12:23 PM

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
...and disappointed that you didn't use mathematica instead.

[/ QUOTE ]
Oh my aching ass. Not to go all uber-nerd on everybody here, but this is just a stupid, stupid comment.

[/ QUOTE ]
Whats wrong with Mathematica?

[/ QUOTE ]
Oh, Mathematica's fine. Fine in the way that a Kia Sephia is fine. It'll probably get you there, but it won't be comfortable and it sure as hell won't be fun. Matlab's like a Porsche Carrera 4 sitting next to the Mathematica Kia Sephia.

hobbsmann

06-21-2005, 12:56 PM

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
...and disappointed that you didn't use mathematica instead.

[/ QUOTE ]
Oh my aching ass. Not to go all uber-nerd on everybody here, but this is just a stupid, stupid comment.

[/ QUOTE ]
Whats wrong with Mathematica?

[/ QUOTE ]
Oh, Mathematica's fine. Fine in the way that a Kia Sephia is fine. It'll probably get you there, but it won't be comfortable and it sure as hell won't be fun. Matlab's like a Porsche Carrera 4 sitting next to the Mathematica Kia Sephia.

[/ QUOTE ]
Well when it comes to solving anything analytically the Kia Sephia smokes the Porsche.

durron597

06-21-2005, 02:11 PM

Substitution
Elimination
Cramers Rule
Matrix Inversion
Graphing

wmspringer

06-21-2005, 02:17 PM

[ QUOTE ]
[ QUOTE ]
Yup, Cramer's rule is matrices (x=Dx/D)

If I was solving it three different ways I'd do:
1) substitution
2) elimination
3) Cramer's rule
.
.
.
4) Matlab /images/graemlins/grin.gif

[/ QUOTE ]

I don't follow?

[/ QUOTE ]

I was saying that 1..3 are probably the easiest ways to do it by hand...but if you wanted to cheat you'd use Matlab :-)

vulturesrow

06-21-2005, 03:33 PM

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
4) Matlab

[/ QUOTE ]

This is actually choice #1 for we liberal arts majors (I was Econ) who were forced to take technical courses. /images/graemlins/grin.gif

[/ QUOTE ]

as an engineer i am impressed if you actually learned matlab.

[/ QUOTE ]

Well I had a roommate who was mechanical engineering major. And after reading the rest of posts, I am starting to think it may have been mathematica that I used. Anyhow, it was one of the two and with a little assistance from my roommate I as able to learn enough to use it to help me flounder through the harder math courses that I had to take. Incidentall these course probably wouldnt seem very hard to a lot of people that post here. But if you take me anywhere beyond probability and statistics I get lost pretty fast. /images/graemlins/smile.gif