1/(1*2)+1/(1*2*3)+1/(1*2*3*4)+.+1/(1*2*3*4*...*50)怎么做?

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1/(1*2)+1/(1*2*3)+1/(1*2*3*4)+.+1/(1*2*3*4*...*50)怎么做?

原式=1/(2*3/2)+1/(3*4/2)+……+1/(50*51*/2)
=1/2*(1/2-1/3+1/3-1/4+……+1/50-1/51)
=1/2*(1/2-1/51)
=49/204