MathDB
angle less than 30 degree

Source: Iran second round 2011

April 28, 2011
linear algebramatrixtrigonometrygeometryangle bisectorgeometry proposed

Problem Statement

In triangle ABCABC, we have ∠ABC=60\angle ABC=60. The line through BB perpendicular to side ABAB intersects angle bisector of ∠BAC\angle BAC in DD and the line through CC perpendicular BCBC intersects angle bisector of ∠ABC\angle ABC in EE. prove that ∠BED≤30\angle BED\le 30.
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