Problem

Source: Russian TST 2014, Day 10 P3 (Groups A & B)

Tags: algebra, trigonometry, minimum value



Let $x,y,z$ be real numbers. Find the minimum value of the sum \begin{align*}|\cos(x)|+|\cos(y)|+|\cos(z)|+|\cos(x-y)|+|\cos(y-z)|+|\cos(z-x)|.\end{align*}