Solve the system using the linear combo. method plz help!!=]

[travispastrana<3]

Solve the system using the linear combination method.
The problem is:

5x - 4y + 4z = 18
-x + 3y - 2z = 0
4x - 2y + 7z = 3

Ok so I was working it out and then I got really confused. Here's what I got. Could someone please tell me where I'm going wrong and explain. Thanks.

-5x + 15y - 10z = 5
5x - 4y + 4z = 18
-----------------------
11y + 6z = 23




-4x + 12y - 8z = 4
4x - 2y+ 7z = 3
----------------------
10y + z = 7


Then I used those two answers for this:

11y + 6z = 23
-60y + -6z = -42
---------------------
-49z = -19

and then z comes out to some weird number but it's not right.
I know that I still have to go and solve for x and y too.
I just got stuck here.

Thanks in advance =]]

 

[galactus]

Re: Solve the system using the linear combo. method plz help

Solve the system using the linear combination method.
The problem is:

5x - 4y + 4z = 18
-x + 3y - 2z = 0
4x - 2y + 7z = 3

Ok so I was working it out and then I got really confused. Here's what I got. Could someone please tell me where I'm going wrong and explain. Thanks.

-5x + 15y - 10z = 0-->Here, this is one small error. 5*0 is not 5, it's 0
5x - 4y + 4z = 18
-----------------------
11y - 6z = 18




-4x + 12y - 8z = 0
4x - 2y+ 7z = 3
----------------------
10y - z = 3


Then I used those two answers for this:

11y - 6z = 18
-60y + 6z = -18
---------------------
-49y = 0

Hence, y=0

Now, back sub to find x and z. They'll be nice integers.

and then z comes out to some weird number but it's not right.
I know that I still have to go and solve for x and y too.
I just got stuck here.

Thanks in advance =]]

 

[travispastrana<3]

Thanks for pointing out that mistake.
I went back and changed it but I still got a wierd answer.

This whole thing is really confusing.
I sorta got it in class but now i'm drawing a blank.

=]]

_______
Thanks!
_______

 

[galactus]

Check again. I edited the post. Pointed out the little gremlins that cause trouble in these sort of problems.

 

[travispastrana<3]

That makes a lot more sense.
Thank you so much for your help!!! =]]]

Sweet. I went back and fixed everything and I got (6,0,-3)
I looked in the back of the book and that's right. =]]

Once again, thank you so much :]