(1/2)*5+(1/5)*8+(1/8)*11+(1/11)*14+(1/14)*17+(1/17)*20

问题描述:

(1/2)*5+(1/5)*8+(1/8)*11+(1/11)*14+(1/14)*17+(1/17)*20

亲,你是要写1/2×5+1/5×8+……+1/17×20吗?
如果是,那么=1/3×(1/2-1/5+1/5-1/8+……+1/17-1/20)
=1/3×(1/2-1/20)=3/20