对于任何非零实数a,b,定义运算“*”如下：a*b=(a-b)/ab,求:2*1+3*2+...+10*9的值
人气：366 ℃ 时间：2019-08-20 21:14:20
解答
a*b=(a-b)/ab可得
n*(n-1)=1/(n(n-1))=1/(n-1)-1/n
所以 2*1+3*2+...+10*9
=1-1/2+1/2-1/3+.+1/8-1/9+1/9-1/10
=1-1/10=9/10
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