1/2+1/6+1/12+1/20+……+1/90等于多少?

题目详情

▼优质解答

答案和解析

1/2+1/6+1/12+1/20+……+1/90
=1/1*2+1/2*3+1/3*4+1/4*5+...+1/9*10
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+...+1/9-1/10
=1-1/10
=9/10

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