math(algebra 1)

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i don't get these please help me:
use the subtitution method to solve the linear system
1)3x+y=0 x-y=4
2)y=-3x-1 x-3y=3
3)3x-y=9 2x+y=6
4)x-2y=0 3x+y=0
Thank you!!:)

  • math(algebra 1) -

    1)3x + y = 0, x - y = 4
    Pick and equation, and solve for either x or y

    x - y = 4
    x = 4 + y

    Substitute, x = 4 + y, for x, in the other equation and solve for y
    x = 4 + y
    3x + y = 0
    3(4 + y) + y = 0
    12 + 3y + y = 0
    12 + 4y = 0
    4y = -12
    y = -3

    substitute y = -3 in either equation to find x
    x - y = 4
    x - (-3) = 4
    x + 3 = 4
    x = 1

    Now you try the others

  • math(algebra 1) -

    so are these correct?
    2)y=-3x-1 x-3y=3
    x=0 y=-1???
    3)3x-y=9 2x+y=6
    dont know help??
    4)x-2y=0 3x+y=0
    please help!!! i don't know how you changed x - y = 4 to x = 4 + y tell me please
    Thanks!!

  • math(algebra 1) -

    2) you are correct

    x - y = 4
    add + y to both sides
    x - y + y = 4 + y
    x = 4 + y

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