Geometry · Equilateral triangle · 30 60 90 triangle · Foot of perpendicular · Triangle area

Problem 4, 2008

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The equilateral triangle \(ABC\) has sides of length \(4\) cm. Let \(D\) be the midpoint of the side \(AB\), and let \(E\) and \(F\) be the feet of the perpendiculars dropped from \(D\) to the sides \(BC\) and \(AC\). Compute the area of the triangle \(DEF\).

A B C D F E
The shaded triangle \(DEF\) is the one whose area is asked for.

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Slovenian High School Mathematics Competition for Vega Awards (MaSSA), izbirno (selection) round 2008, 1. letnik, category A, problem 4. Organized by DMFA Slovenije (Society of Mathematicians, Physicists and Astronomers of Slovenia). Source