MathDB
Triangles with Equal Area

Source: 2010 IrMO Paper 2 Problem 5

January 30, 2018
geometry

Problem Statement

Suppose a,b,ca,b,c are the side lengths of a triangle ABCABC. Show that x=a(b+ca),y=b(c+ab),z=c(a+bc)x=\sqrt{a(b+c-a)}, y=\sqrt{b(c+a-b)}, z=\sqrt{c(a+b-c)} are the side lengths of an acute-angled triangle XYZXYZ, with the same area as ABCABC, but with a smaller perimeter, unless ABCABC is equilateral.