>>858 >>865
訂正
V1=z_1+z_10=2cos(2π/11)
V2=z_2+z_9=2cos(4π/11)
V3=z_3+z_8=2cos(6π/11)
V4=z_4+z_7=2cos(8π/11)
V5=z_5+z_6=2cos(12π/11)=-2cos(π/11)