y = –a is the correct solution. The other suggested solution does not work, because that equation is not satisfied by the coordinates of R.

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- Sep 2nd 2010, 07:14 PM #1

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- Jul 2009
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## Locous Question

Find the locous of the intersection of tangents at R, given

P (2ap, ap^2) and Q (2aq, aq^2) are points on 4ay = x^2

Given that tangents are y = px - ap^2 and y = qx - aq^2

and PQ is a focal chord, passing through (0,a) meaning pq = -1

The point of intersection R is (a(p+q), apq)

is the locus y = -a ? or is it different, as in y = qx/ (1-q^2) as suggested by an answer?

- Sep 2nd 2010, 11:37 PM #2