1/2 +1/6+1/12+1/20+...+1/110=1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)+...+1/(10×11)=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+...+1/10-1/11=1-1/11=10/11 应该是10/11,分数线“/”左边是分子,右边是分母.