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    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!
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    Adding 1 and 5*(3) doesn't get rid of the z's. You need to substract 1 and 5*(3).
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    (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???
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    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 ..
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    (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??
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    Id use matrices (if you've done it that way before)
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    (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??
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    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
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    And yes, he's right you have to add (1) to (3) not subtract
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    (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.
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    (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???
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    (Original post by JLou01)
    So is my method correct then???
    Well I haven't checked your arithmetic but it looks correct.
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    (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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