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Math Help - If AB passes through the point (2,3) and is perpendicular to y= 2x-7, find the equati

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    If AB passes through the point (2,3) and is perpendicular to y= 2x-7, find the equati

    If AB passes through the point (2,3) and is perpendicular to y= 2x-7, find the equation of AB in general form.
    Please either provide the process of doing so, or help me work through it. Anything would be appreciated. I know itís probably quite simple, but I canít seem to understand this problem. Thank you for your help!
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  2. #2
    MHF Contributor alexmahone's Avatar
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    For 2 perpendicular lines, product of slopes is -1.

    m_1=2
    m_2=-\frac{1}{2}

    Slope of AB is -\frac{1}{2}

    y=-\frac{1}{2}x+C
    This line passes through (2,3).
    3=-\frac{1}{2}*2+C
    3=-1+C
    C=4

    The equation of AB is y=-\frac{1}{2}x+4
    Last edited by alexmahone; May 31st 2009 at 01:48 AM.
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    A reply for Alex

    Alex,

    I do not understand what general form means. Apparently you have not given me the answer in general form, as I in fact have the answer, which is:

    x+2y-8= 0

    How do I obtain this answer?
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    Quote Originally Posted by JadeKiara View Post
    Alex,

    I do not understand what general form means. Apparently you have not given me the answer in general form, as I in fact have the answer, which is:

    x+2y-8= 0

    How do I obtain this answer?
    Hmmm... This is strange. You are learning co-ordinate geometry, so you are expected to know basic algebra!

    Is it hard to manipulate y=-\frac{1}{2}x+4 to get x + 2y - 8 = 0?

    I guess you should review basic algebra first. That will help you a lot in Co-ordinate geometry.
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    Well, it is certainly strange to know that we have not done that in class. Maybe the teacher is attempting to challenge us? I do not know. I have researched the general form, and thus obtained the following formula: ax + by = C

    Can you explain how to do this operation please?
    Last edited by JadeKiara; May 31st 2009 at 02:50 AM.
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  6. #6
    MHF Contributor alexmahone's Avatar
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    y=-\frac{1}{2}x+4
    Multiply throughout by 2
    2y=-x+8
    x+2y-8=0
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    Lightbulb

    Thank you Alex. It is beyond me why I have not learnt that, seeing as it is essential to do so. No wonder why I couldn't do it!

    Anyway, I have researched the conversion of the two forms now, and hopefully I won't have that trouble in the future.

    Thank you once again!

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