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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?
  2. jcsd
  3. Jan 11, 2007 #2


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


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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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