則iS=i2+2i3+3i4…+1999i2000+2000i2001 ②,
①減去②且錯(cuò)位相減 可得 (1-i)S=i+i2+i3+…+i2000-2001i2001=
i(1?i2000) |
1?i |
i(1?1) |
1?i |
∴S=
?2000i |
1?i |
?2000i(1+i) |
(1?i)(1+i) |
?2000i+2000 |
2 |
故答案為:1000-1000i.
i(1?i2000) |
1?i |
i(1?1) |
1?i |
?2000i |
1?i |
?2000i(1+i) |
(1?i)(1+i) |
?2000i+2000 |
2 |