①当n=2k,k∈Z时, sin(nπ+2π/3)·cos(nπ+4π/3) = sin(2π/3)·cos(4π/3) = sin(π-π/3)·cos(π+π/3) = sin(π/3)·[-cos(π/3)] =-√3/4 ②当n=2k+1,k∈Z时, sin(nπ+2π/3)·cos(nπ+4π/3) = sin(π+2π/3)·cos(π+4π/3) = sin(2π/3)·cos(4π/3) = sin(π-π/3)·cos(π+π/3) = sin(π/3)·[-cos(π/3)] =-√3/4故：sin(nπ+2π/3)·cos(nπ+4π/3) =-√3/4