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# Simultaneous Equations Help watch

1. Hey, could someone please check if my method is correct, and if not, tell me what is wrong with it?:

18x - 2y + 5z = -4......................(1)
29x + 14y - 5z = -7....................(2)
13x + 2y + z = 3........................(3)

Adding (1) and (2) gives: 47x + 12y = -11................(4)

Subtracting (1) and 5*(3) gives: -47x - 12y = -19...........(5)

Using (4) and (5), this shows that the system is invalid given that 47x + 12y cannot equal both -11 and 19, therefore there is no solution.

I think I have made a mistake though, and there is a solution. Can any1 offer any help??? Thanks!
2. Adding 1 and 5*(3) doesn't get rid of the z's. You need to substract 1 and 5*(3).
3. (Original post by insparato)
Adding 1 and 5*(3) doesn't get rid of the z's. You need to substract 1 and 5*(3).

Why wouldn't it??? Also, how would u do that???
4. 18x - 2y + 5z = -4 - (1)

65x + 10y + 5z = 15 - 5*(3)

Adding them does not get rid of the z's.

Substracting them does, 5z - 5z ..
5. (Original post by insparato)
18x - 2y + 5z = -4 - (1)

65x + 10y + 5z = 15 - 5*(3)

Adding them does not get rid of the z's.

Substracting them does, 5z - 5z ..
Oh, sorry thats what I meant, and I did that, and it end up with no solution. Have I gone wrong somewhere else??
6. Id use matrices (if you've done it that way before)
7. (Original post by Necro Defain)
Id use matrices (if you've done it that way before)
No, I haven't. Is there any other way??
8. Eliminate one varialble by adding/subtracting equations 1 with 2 and 2 with 3, then eliminate another one from the remaining two equations to get an answer, then just sub back in to the other expressions to find the other 2 answers
9. And yes, he's right you have to add (1) to (3) not subtract
10. (Original post by JLou01)
No, I haven't. Is there any other way??
There is no solution to find. The equations are inconsistent.

This means that they are the equations of 3 planes that have no point in common.
11. (Original post by Mr M)
There is no solution to find. The equations are inconsistent.

This means that they are the equations of 3 planes that have no point in common.
So is my method correct then???
12. (Original post by JLou01)
So is my method correct then???
Well I haven't checked your arithmetic but it looks correct.
13. (Original post by Mr M)
Well I haven't checked your arithmetic but it looks correct.
Thanks very much, I finally get an answer!!!

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Updated: November 9, 2008
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