<Solid-2026-275>, hint

 

<Solid-2026-275> tetrahedron, area

<Taiwan MO 1997>

 

<Tri-2026-2815>, hint

Consider equilateral triangle ABC and a right triangle 30-60-90. 

<Tri-2026-2815>, general, median

<Taiwan MO 1997>

 

<Cir-2026-815>, hint