Harcourt's theorem - Nikolaos Dergiades and Juan Carlos Salazar We give a proof of Harcourt's theorem that if the signed distances from the vertices of a triangle of sides a, b, c to a tangent of the incircle are a_1, b_1, c_1, then aa_1 + bb_1 + cc_1 is twice of the area of the triangle. We also show that there is a point on the circumconic with center I whose distances to the sidelines of ABC are precisely a_1, b_1, c_1. An application is given to the extangents triangle formed by the external common tangents of the excircles. ✪ ✪ ✪ ✪ ✪ Link tải tài liệu: LINK TẢI TÀI LIỆU Theo LTTK Education
