MathDB
right angle wanted, 3 altitudes

Source: All-Russian MO 2009 Regional 9.3

August 27, 2024
geometryright angleperpendicular

Problem Statement

In an acute triangle ABCABC the altitudes AA1AA_1, BB1BB_1, CC1CC_1 are drawn. A line perpendicular to side ACAC and passing through a point A1A_1, intersects the line B1C1B_1C_1 at point DD. Prove that angle ADCADC is right.
Back to ProblemsView on AoPS