1/6+1/12+1/20+1/30+.+1/72=?
问题描述:
1/6+1/12+1/20+1/30+.+1/72=?
答
1/6+1/12+1/20+1/30+.+1/72
=1/2*3+1/3*4+...+1/8*9
=1/2-1/3+1/3-1/4+.+1/8-1/9
=1/2-1/9
=7/18