作业帮1/(1*2)+2/(1*2*3)+3/(1*2*3*4)+.+8/(1*2*3*4*5*6*7*8*9)=?
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1/(1*2)+2/(1*2*3)+3/(1*2*3*4)+.+8/(1*2*3*4*5*6*7*8*9)=?
1/(1*2)+2/(1*2*3)+3/(1*2*3*4)+.+8/(1*2*3*4*5*6*7*8*9)=?
1/(1*2)+2/(1*2*3)+3/(1*2*3*4)+.+8/(1*2*3*4*5*6*7*8*9)=?
（1）预备知识：n/[(n+1)!]=[(n+1)-1]/[(n+1)!]=[1/n!]-[1/(n+1)!].(2)原式=1-（1/9!)=(9!-1)/9!.