Geodesic
Seven Geometric Problems
Matematičeskoe obrazovanie, no. 4 (2009), pp. 2-10 
V. B. Drozdov. Seven Geometric Problems. Matematičeskoe obrazovanie, no. 4 (2009), pp. 2-10. http://geodesic.mathdoc.fr/item/MO_2009_4_a0/
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     author = {V. B. Drozdov},
     title = {Seven {Geometric} {Problems}},
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     year = {2009},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MO_2009_4_a0/}
}
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Voir la notice de l'article provenant de la source Math-Net.Ru

Let G be the mass center of a triangle, H be the orthocenter, and L be the center of the inscribed circle. The conditions for GH, GL, HL to be parallel o r / a n d orthogonal to a side of the triangle are analyzed. The exposition is based on vector approach.