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1/1*3+1/2*4+1/3*5+1/4*6+1/5*7+1/6*8------1/17*19+1/18*20 怎样做
人气:199 ℃ 时间:2019-08-22 18:07:42
解答
1/1*3+1/2*4+1/3*5+1/4*6+1/5*7+1/6*8------1/17*19+1/18*20
=1/2(1-1/3+1/2-1/4+1/3-1/5+1/4-1/6+%1/17-1/19+1/18-1/20)
=1/2×(1-1/19+1/2-1/20)
=1/2×(18/19+9/20)
=1/2×531/380
=531/760
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