Question

(Still not answered) Please help me solve this system:
6x-y+3z=-9
5x+5y-5z=20
3x-y+4z=-5
I understand how to solve these problems, but this one is not making sense.

Answer 1

your life will probably be easier if you replace the middle one by \[x+y-z=4\]

Answer 2

i find these amazingly tedious, either with a matrix or eliminating variables one at a time
if i were you, i would cheat

Answer 3

http://www.wolframalpha.com/input/?i=6x-y%2B3z%3D-9,+5x%2B5y-5z%3D20,+3x-y%2B4z%3D-5

Answer 4

@satellite73 Do you know how the calculator got the answer? I'm trying to understand the how, not the what.

Answer 5

this works for me;
use 2 equations and eliminate one variable by using an expression with the other 2 variables.
use another 2 equations but eliminate the same variable you eliminated before.
now you can solve a regular simultanuous equation with 2 variables.
go back and find the value of the eliminated variable.
good practice to check your values in either of the originals. it is extremely easy to make simple errors when doing simultaneous equations.