1-3/2+5/6-7/12+9/20-11/30+.-19/90+21/110=?
问题描述:
1-3/2+5/6-7/12+9/20-11/30+.-19/90+21/110=?
答
每一项可理解为(2a+1)/a(a+1)
=1/a+1/(a+1)
原式=1-1-1/2+1/2+1/3-1/3-1/4...-1/9-1/10+1/10+1/11
=1/11