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Published online by Cambridge University Press: 20 January 2009
1. Let one of the series of circles, which can be drawn so as to touch the sides AB, AC of a triangle, touch those sides in K, L; and let AK = AL = δ.
Then the points K, L are

and the lines BL, CK are givn by

Hence eliminating δ we get for the locus of P the hyperbola

The allied hyperbolas are

* The mode of procedure adopted in the following paragraphs is the same, viz., p, q, r points are on BC, CA, AB respectively.
† The polars of (–1, 1, 1), (1, – 1, 1), (1, 1, – 1) are respectively
(∴ this is the isogonal conjugate of the polar of the incentre),