1—1/2+1/6+1/12+1/20+.+1/72+1/90
问题描述:
1—1/2+1/6+1/12+1/20+.+1/72+1/90
答
原式=1-1/2+1/2*3+1/3*4+……+1/9*10
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+……+(1/9-1/10)
=1-1/10
=9/10