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Math Help - Few Questions on Systems of Linear Equations

  1. #1
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    Few Questions on Systems of Linear Equations

    I have a few questions on systems of linear equations. I tried them and either i get a negative answer that should be positive, or vice versa. I checked the answers on the back of the textbook and answers were different than mine. Please help.

    Solve by elimination.
    38=2x-5y
    75=7x-3y

    What i did to solve:
    -7(38=2x-5y) 2((75=7x-3y)
    -266=-14x+35y 150=14x-6y

    150= 14x-6y
    +(-266= -14x+35y)
    -116 = 29y
    -116/-29
    y= 4

    I use the same process to find x. x=-9

    my answer (x,y) = (-9,4)
    textbook answer (x,y) = (9,-4)

    what did i do differently? where did i go wrong? help
    __________________________________________________ _________________________

    Solve by elimination:
    x/3+y/4=2
    2x/3-y/2=0

    how do i break this down to solve?
    i tried and ended up with y=2, text said x,y = 3,4
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  2. #2
    MHF Contributor MarkFL's Avatar
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    Re: Few Questions on Systems of Linear Equations

    Where you have:

    -116 = 29y
    -116/-29 = y

    You should have:

    -116 = 29y
    -116/29=y

    Do you see why, and how this fixes your error?

    For the second system, multiply the first equation by 12 and the second by 6 to get:

    4x+3y=24

    4x-3y=0

    Can you finish?
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  3. #3
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    Re: Few Questions on Systems of Linear Equations

    Quote Originally Posted by MarkFL2 View Post
    Where you have:

    -116 = 29y
    -116/-29 = y

    You should have:

    -116 = 29y
    -116/29=y

    Do you see why, and how this fixes your error?
    but when you bring the 29 over, why doesn't it change to -29? i dont understand
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  4. #4
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    Re: Few Questions on Systems of Linear Equations

    if you subtract 29 from both sides, it becomes -29 ... you are dividing by 29, not subtracting
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    Re: Few Questions on Systems of Linear Equations

    Thanks. No wonder i keep making mistakes
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