解:20×20-19×19+18×18-17×17+……+2×2-1×1
=(20+19)×(20-19)+(18+17)×(18-17)+……+(2+1)×(2-1)
=210
2024-10-31
2024-10-30
2024-10-29
2024-10-28
2024-10-25
2024-10-24
2024-10-23