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Homework Help: Coordinate Geometry

  1. Jan 11, 2007 #1
    The points P(cp,c/p) and Q(cq,c/q) lie on the rectangular hyperbola xy=c^2. Show that the equation of the chord PQ is pqy+x=c(p=q), and deduce the equation of the tangent at the point P.

    I can do the proving. And I can find the tangent as well if the word "deduce" is not there. How can you deduce the equation by refering to the chord PQ?
     
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  3. Jan 11, 2007 #2

    Gokul43201

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    - post deleted...I was talking out of my hat -
     
    Last edited: Jan 11, 2007
  4. Jan 11, 2007 #3

    HallsofIvy

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    You mean pqy+ x= c(p-q). Remember that we can think of a tangent, at P, as being the "limit" of the chords as q goes to p. Take the limit as q goes to p of pqy+ x= c(p- q).
     
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