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Math Help - Substitution method

  1. #1
    Member Mr Rayon's Avatar
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    Talking Substitution method

    Find the points of intersection between the following equations for straight lines using the substitution method.

    y=x+5 and 5x-y=-1

    &

    y=x-3 and 2x-y=7
    thx
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  2. #2
    Super Member angel.white's Avatar
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    Quote Originally Posted by Mr Rayon View Post
    Find the points of intersection between the following equations for straight lines using the substitution method.

    y=x+5 and 5x-y=-1

    &

    y=x-3 and 2x-y=7
    thx
    EQ1:
    You know that y=x+5, so substitute "x+5" in for y in the other equation

    5x-y=-1
    5x-(x+5)=-1
    5x-x-5=-1
    4x-5=-1
    4x=4
    x=1

    Now just substitute "1" in for x in either equation

    5x-y=-1
    5(1)-y=-1
    5-y=-1
    -y=-6
    y=6

    Now you try for the second equation.
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  3. #3
    Member Mr Rayon's Avatar
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    Is this right?

    y=x-3
    2x-y=7
    2x-(x-3)=7
    2x-x+3=7
    x+3=7
    -3 -3
    x=4
    y=4-3
    y=1

    So x=4 and y=1 (4,1)
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Mr Rayon View Post
    Is this right?

    y=x-3
    2x-y=7
    2x-(x-3)=7
    2x-x+3=7
    x+3=7
    -3 -3
    x=4
    y=4-3
    y=1

    So x=4 and y=1 (4,1)
    Yep, you got it!

    -Dan
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  5. #5
    Junior Member
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    oh i understand now
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