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12 January, 15:37

3x-y=7

9x-3y=21

how do I do it by the substitution method i think so.?

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  1. 12 January, 15:59
    0
    3x-y=7

    9x-3y=21

    9x-3y=21

    Put the equation into slope intercept form so that you can later substitute it into 3x-y=7.

    9x-3y=21

    -9x. - 9x

    -3y=-9x+21

    Divide each number by - 3.

    You get y=3x-7

    You will substitute y for 3x-7 in 3x-y=7

    Solve:

    3x - (3x-7) = 7

    3x-3x+7=7

    0+7=7

    7=7

    This means that both equations are the same.
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