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Math Help - Find equation of line (simple question)

  1. #1
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    Find equation of line (simple question)

    Hello,

    I'm doing revision for a test and this problem has slipped my mind.

    "Find an equation of the line passing through the point (3,1) and parallel to the line '3x - y - 4 = 0'.

    From what I understand, I need to isolate y.

    3x-y-4 turns into y = 3x - 4 (I'm assuming).

    Then, because the line is parallel, the slope is the same (3). This is where I'm falling down...Obviously with this equation, the points given don't add up. Based on the answer, I'm supposed to get y=3x - 8, but I'm not sure what I'm doing wrong.

    Any points in the right direction?
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  2. #2
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    Re: Find equation of line (simple question)

    y = 3x +c

    1 = 3(3) +c

    -8 = c

    therefore we get y = 3x -8
    Thanks from astuart
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  3. #3
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    Re: Find equation of line (simple question)

    Quote Originally Posted by Goku View Post
    y = 3x +c

    1 = 3(3) +c

    -8 = c

    therefore we get y = 3x -8
    Right, knew it was simple!

    Thanks.
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  4. #4
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    Re: Find equation of line (simple question)

    When you do not have the y-intercept you could use the eqn:
    y-b=m(x-a) where (a,b) is a point which lies on the line, and m is the gradient.
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