MathDB

G1

Part of 2010 Balkan MO Shortlist

Problems(1)

pentagon with A=B=C=D=120

Source:

5/15/2010
Let ABCDEABCDE be a pentagon with A^=B^=C^=D^=120∘\hat{A}=\hat{B}=\hat{C}=\hat{D}=120^{\circ}. Prove that 4⋅AC⋅BD≥3⋅AE⋅ED4\cdot AC \cdot BD\geq 3\cdot AE \cdot ED.
trigonometrygeometry unsolvedgeometry