数列0.5,0.55,0.555,0.5555,……,0.5555555555(n个5),……的前n项和为?
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数列0.5,0.55,0.555,0.5555,……,0.5555555555(n个5),……的前n项和为?
数列0.5,0.55,0.555,0.5555,……,0.5555555555(n个5),……的前n项和为?
数列0.5,0.55,0.555,0.5555,……,0.5555555555(n个5),……的前n项和为?
2 1 n n
Sn=5/9[(1/ 10) (10 -1)+…(1/10) (10 -1)]
2 n
=5 /9[1-(1/10 ) +1 -(1/10) +…+1-(1/ 10) ]
n
=5 /9[n +(1-10 )/ 90]
原谅跳步,实在不好打,化简自己来吧.好累啊