3

Part of 2003 Nordic

Problems(1)

right triangle out of an interior point of an equilateral

Source: Nordic Mathematical Contest 2003 #3

{D}

inside the equilateral triangle

{\triangle ABC}

{\angle ADC = 150^o}

. Prove that a triangle with side lengths

{|AD|, |BD|, |CD|}

is necessarily a right-angled triangle.

Equilateral Triangleright trianglesgeometry