Объясните подробно решение, с пи (плохо знаю эту тему). :

5π/3 = π + 2π/3
13π/6 = 2π + π/6
7π/6 = π+ π/6
подставим эти замены
ctg (5π/3) *cos(13π/6)*sin(7π/6) = ctg (π + 2π/3)*cos(2π + π/6)*sin(π+ π/6)=
= -ctg (2π/3)*cos(π/6)*(-sin(π/6)) = 1/2* ctg (2π/3)*2cos(π/6)*sin(π/6)=
=1/2ctg (2π/3)*sin(π/3)=1/2 * 1/√3* √3/2 = 1/4=0,25