=1/1*2-1/2*3+1/2*3-1/3*4+1/3*4-1/4*5+……+1/28*29-1/29*30
=1/1*2-1/29*30
=217/435详细解析 谢谢2/a(a+1)(a+2)=1/a(a+1)-1/(a+1)(a+2)