The figure shows a triangle ABC with the
excircle EA tangent to the sides at the points A', B' and C'. Prove that AA', BB',
and CC' are concurrent at a point GA called Gergonne external point.
Joseph Diez Gergonne (1771-1859) was a French mathematician and geometer who founded Annales de mathematiques in 1810.
![Gergonne Points, Excircles, Concurrency](p682_gergonne_point_ex.gif)
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