原式=(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)=434/870=217/435
2/1*2*3=1/1*2-1/2*32/2*3*4=1/2*3-1/3*4以此类推原式=1/1*2-1/2*3+1/2*3-1/3*4+……+1/28*29-1/29*30=1/1*2-1/29*30=217/435