5*10\1+10*15\1+15*20\1+.+35*40\1+40*45\1怎么做
人气:147 ℃ 时间:2020-01-27 07:16:40
解答
1/5*10+1/10*15+1/15*20+...+1/35*40+1/40*45
=(1/25)(1/1*2+1/2*3+1/3*4+...1/7*8+1/8*9)
=(1/25)(1-1/2+1/2-1/3+1/3-1/4+...+1/7-1/8+1/8-1/9)
=(1/25)(1-1/9)
=(1/25)(8/9)
=8/225
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