设{An}是等差数列,已知A1=100,d=_2求S20
问题描述:
设{An}是等差数列,已知A1=100,d=_2求S20
答
S20=100×20+20×19×2=2760d等于负二哦S20=100×20+20×19×(-2)=1240
设{An}是等差数列,已知A1=100,d=_2求S20
S20=100×20+20×19×2=2760d等于负二哦S20=100×20+20×19×(-2)=1240