sinπ/14 sin3π/14 sin5π/14= cos6π/14 cos4π/14 cos2π/14 =cosπ/7 cos2π/7 cos3π/7……(1) 因为2sinθcosθ=sin2θ, 又sin3π/7=sin4π/7,sin6π/7=sinπ/7所以 (1)*sinπ/7= sinπ/7 cosπ/7 cos2π/7 cos...