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Math Help - Solve the system by substitution

  1. #1
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    Solve the system by substitution

    I am really stuck on this one.


    3x 5y = 9
    y = 3x + 3
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Patience View Post
    I am really stuck on this one.


    3x – 5y = 9
    y = 3x + 3
    3x – 5y = 9 ........................(1)
    y = 3x + 3 .....................(2)

    from (2) we see y = 3x + 3, substitute 3x + 3 for y in (1), we get:
    3x – 5y = 9
    => 3x - 5(3x + 3) = 9
    =>3x - 15x - 15 = 9
    => -12x = 24
    => x = -2

    but y = 3x + 3
    => y = 3(-2) + 3
    => y = -3

    so x = -2, y = -3
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