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    KDRGV5's Avatar
    KDRGV5 Posts: 1, Reputation: 1
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    #1

    Feb 5, 2009, 10:05 PM
    algebra substitution
    x + 2y = 13
    3x - 5y = 6

    I'm getting lost with this problem. I started adding the two equations together and I wanted to make sure I had done it correctly

    4x-3y=19
    x-3y=15
    I'm not sure where to go from here.

    when substitution problems have 2 equations, 1 of the problems have to be solved for x or y and then substituted back into the problem?
    ISneezeFunny's Avatar
    ISneezeFunny Posts: 4,175, Reputation: 821
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    #2

    Feb 5, 2009, 10:33 PM

    you don't have to add/subtract equations.

    first equation

    x + 2y = 13

    x = 13 - 2y

    then take this value for x, and put it in the second equation, and solve for y.
    sarnian's Avatar
    sarnian Posts: 462, Reputation: 9
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    #3

    Feb 7, 2009, 07:31 AM
    You have :

    x + 2y = 13
    3x - 5y = 6

    You can not solve both values for x and y at once.
    You first have to eliminate either x or y in both equations.
    So if we eliminate x , you need to multiply all values of equation 1 with 3, to get the value of 3x

    x + 2y = 13
    3 (x + 2y) = 3 . 13
    3x +6y = 39
    3x = 39 - 6y

    Now substitute that value of 3x in the second equation (3x - 5y = 6)

    39 - 6y - 5y = 6

    and work out the value of y
    Once you have the value of y , you can use the first equation to work out the value of x

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