题目
这道题等于多少?3/(2*3)+3/(3*4)+3/(4*5)+3/(5*6)+……+3/(19*20)=
提问时间:2020-08-10
答案
3/(2*3)+3/(3*4)+3/(4*5)+3/(5*6)+……+3/(19*20)
=3(1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+……+1/(19*20))
=3(1/2 -1/3 +1/3-1/4..+1/19-1/20)
=27/20
=3(1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+……+1/(19*20))
=3(1/2 -1/3 +1/3-1/4..+1/19-1/20)
=27/20
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