Evaluation cos faction / 7 * Cos2 faction / 7 * cos3 / 7 faction who will help do the next 3Q

Evaluation cos faction / 7 * Cos2 faction / 7 * cos3 / 7 faction who will help do the next 3Q

Original formula = sin π / 7 * cos π / 7 * Cos2 π / 7 * cos3 π / 7 / sin π / 7
=2sinπ/7*cosπ/7*cos2π/7*cos(π-4π/7)/2sinπ/7
=sin2π/7*cos2π/7*(-cos4π/7)/2sinπ/7
=-2sin2π/7*cos2π/7*cos4π/7/4sinπ/7
=-sin4π/7*cos4π/7/4sinπ/7
=-2sin4π/7*cos4π/7/8sinπ/7
=-sin8π/7/8sinπ/7
=sinπ/7/8sinπ/7
=1/8