通常用待定系数法,可设1/n*(n+1)*(n+2)=a/n+b/(n+1)+c/(n+2)两边去掉分母后对比各项系数,解出系数即可.1/n*(n+1)*(n+2)=0.5/n-1/(n+1)+0.5/(n+2)Sn=[1-1/2-1/(n+1)+1/(n+2)]/2=[1/2-1/(n+1)+1/(n+2)]/2...