|2+2e^(2πi/5)+e^(6πi/5)| ＝|2+2cos(2π/5)+cos(6π/5)+i(2sin(2π/5)+sin(6π/5))| ＝√[(2+2cos(2π/5)-cos(π/5))^2+(2sin(2π/5)-sin(π/5))^2] ＝√[9+8cos(2π/5)-8cos(π/5)] ＝√[9-16sin(3π/10)sin(π/10)] ＝√(9-16vos36°cos72°) ＝√[9-(16sin36°cos36°cos72°/sin36°)] ＝√[9-(4sin144°/sin36°)] ＝√5。
答：建议上h55和4850能控制成本详情>>
答：详情>>
