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-   -   Quick math question.... (http://forums.netphoria.org/showthread.php?t=564)

obscured01 10-01-2002 12:39 PM
Quick math question....
 
Ok... I have 3 systems, with 3 variables, x,y,and z. Can I use cramer's rule to solve this? Or must I go through and figure the matrices to get the answer to the x, y and z variables?

Here's the equations:

2x + 3y 0z = 800
3x + 0y +3z = 650
0x + 1y ***z = 350

I know there has to be an easier way to solve this without having to put it into a matrix. I would use subsitution if I knew how to do that with 3 equations...

I was absent the day we went over this in class and it doesn't explain how in the book... we have a quiz today... help?


------------------
~*Sarah Kimberly*~

...and the tragic and
romantic ascent...

AIM: Gazing Iscariot

[This message has been edited by obscured01 (edited 10-01-2002).]

obscured01 10-01-2002 01:05 PM
*bump* help http://www.netphoria.org/wwwboard/frown.gif

scouse_dave 10-01-2002 01:13 PM
i can help...gimme a sec whilst i type some stuff out

scouse_dave 10-01-2002 01:20 PM
cramer's rule doesn't ring a bell in all honesty, maybe when i learnt linear algebra, we called it something else.

regardless, tho, it's probably just a shorthand of sorts for simplifying the system of equations..you can always solve it with normal row/column operations in matrix form

personally, i wouldn't even bother with using matrices as the system is quite simple...it should be fairly obvious to you that with only 3 variables (2 non-zero in each case) the asnwer should fall out pretty quickly

1. multipy row (3) by to get
3y+3z=1050

2. row (3) - row (2) gives
-3x+3y=400
(call this Q)

3. row (1) - Q gives
5x = 200 => x=40

basic substitution should find you y and z

in a sense, this IS using the matrix method without writing out the matrix in each case

hope that's some help

obscured01 10-01-2002 01:21 PM
yes, thank you. I'm stupid when it comes to math if I don't have everything fully explained. Gracias http://www.netphoria.org/wwwboard/smile.gif

------------------
~*Sarah Kimberly*~

...and the tragic and
romantic ascent...

AIM: Gazing Iscariot

scouse_dave 10-01-2002 01:31 PM
Quote:
Originally posted by obscured01:
I would use subsitution if I knew how to do that with 3 equations...
if you're ever in doubt..just pick an equation at random, and substitute it into another of the equations...

it may not always be the most effecient answer, but in cases like this, you'll always get the answer


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