2/1X3+2/3X5+2/5x7+.+2/19x21全过程(最好带原因),
2/1X3+2/3X5+2/5x7+.+2/19x21全过程(最好带原因),
数学人气:550 ℃时间:2019-12-16 19:53:02
优质解答
=2*(1/1*3+1/3*5+.)=2*1/2*(1-1/3+1/3-1/5.+1/19-1/21)=20/21
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