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    purple54 Posts: 1, Reputation: 1
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    #1

    May 28, 2010, 12:04 PM
    substitution and elimination in algebra
    6x + 7y =32
    -4x +y =24
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #2

    May 28, 2010, 10:48 PM

    You need to understand what you need to do.

    In substitution, you are required to replace one variable by its equivalent. What I mean by this is:

    If you know that x = 'something'
    Then, you can replace x in an equation such as x + y = 2, so that it becomes:
    'something' + y = 2

    A more practical example is this:
    x = 2y - 1
    x + y = 2

    Replace the 'equivalent' of x in the second equation: (2y - 1) + y = 2
    Then, you can solve, giving 3y = 3, and y = 1. Replacing the value of y in any equation gives x = 1.

    ~~~~~~~~~~~~~~~~

    In elimination, you add or subtract two equations so that one term is eliminated.
    I'll take the previous example.

    x = 2y - 1
    x + y = 2

    I will now put all the similar terms one under the other. x's under x's and y's under y's with the remaining numbers on the same side, like this:
    x - 2y = -1
    x + y = 2

    Then, the easiest way to eliminate one of the variables is to subtract one equation from the other.

    Code:
    x - 2y = -1
    x +  y =  2 -
    0 - 3y = -3
    This gives again y = 1, and using this value, we get x = 1.

    Can you try this with your problem? Post your answer. :)

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