原式=(1/1-1/2)+(1/2-1/3)+(1/3-1/4)+...+(1/39-1/40)
=1-1/2+1/2-1/3+1/3-1/4+...+1/39-1/40
=1-1/40
=39/40
什么的
1
总共39项,每项用1减然后求结果就是1/2+1/3+1/4.........+1/40=x 然后求解x= 然后答案就是39-x
1/(1×2)+1/(2×3)+……+1/(39×40)
=1-1/2+1/2-1/3+……+1/39-1/40
=1-1/40
=39/40
我们是同级生哦