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Math Help - Double checking and some help

  1. #1
    Junior Member
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    Sep 2008
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    Double checking and some help

    I need help with solving equations with substitution I'm stuck on problem. like

    x=-4y
    3x+2y=20

    and

    y= -x+6
    3x+y=-10

    Can you guys also help me double check these?

    4x+y=1
    y=x-9
    For this I got (2,7)

    5x+y=4
    y=2x-3
    I got (1,-1) for this

    Thanks for your help!
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  2. #2
    Junior Member
    Joined
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    First Problem,
    x=-4y
    3x+2y=20

    Take the first equation and put it into the second where the "x" is.

    3(-4y)+2y=20

    Solve for y. You get.
    -12y+2y=20
    -10y=20
    y=-2

    Second Problem
    y= -x+6
    3x+y=-10

    Take the first equation and put it where the "y" is on the second equation.
    After all that is what "y" equals.

    3x+-x+6=-10

    Solve for the Problem

    2x+6=-10
    2x=-16
    x=-8

    Double Checking
    It is actually (2, -7) and the second one is correct.
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  3. #3
    Junior Member
    Joined
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    Posts
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    Quote Originally Posted by RaphaelB30 View Post
    First Problem,
    x=-4y
    3x+2y=20

    Take the first equation and put it into the second where the "x" is.

    3(-4y)+2y=20

    Solve for y. You get.
    -12y+2y=20
    -10y=20
    y=-2

    Second Problem
    y= -x+6
    3x+y=-10

    Take the first equation and put it where the "y" is on the second equation.
    After all that is what "y" equals.

    3x+-x+6=-10

    Solve for the Problem

    2x+6=-10
    2x=-16
    x=-8

    Double Checking
    It is actually (2, -7) and the second one is correct.
    Thanks for your help! Now putting them in ordered pair, would the first one look like (-8,2) and the second look like (8,-2)?
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  4. #4
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    Joined
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    Quote Originally Posted by Jubbly View Post
    Thanks for your help! Now putting them in ordered pair, would the first one look like (-8,2) and the second look like (8,-2)?
    Yes, that's what it would look like.
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