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Homework Help: Equation of a line problem

  1. Feb 14, 2007 #1
    equation of a line problem!!!

    The points A and B have co-ordinates (3,4) and (7,-6) respectively. the straight line S passes through A and is perpendicular to AB.
    FInd an equation for S, giving your answer in the form ax+by+c=0

    Ok so im really stuck on this question. So far i have calculated the gradient of the line AB by doing (-6-4)/(7-3) and i got -2.5

    But now i dont know what to do please help :rolleyes:
  2. jcsd
  3. Feb 14, 2007 #2
    How are the slopes of perpendicular lines related?
  4. Feb 15, 2007 #3
    i have no idea how the slopes are related
  5. Feb 15, 2007 #4


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    Staff Emeritus
    Science Advisor

    Two lines with gradients m and m' are perpendicular if (m)(m')=-1
  6. Feb 15, 2007 #5
    so would that mean that my gradient is +2.5
  7. Feb 15, 2007 #6
    Would it?

    If m' x (-2.5) = -1, what does m' = ?
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