2/11*13+2/13*15+2/15*17+2/17*19+2/19简便计算
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![2/11*13+2/13*15+2/15*17+2/17*19+2/19简便计算](/uploads/image/z/33939-27-9.jpg?t=2%2F11%2A13%2B2%2F13%2A15%2B2%2F15%2A17%2B2%2F17%2A19%2B2%2F19%E7%AE%80%E4%BE%BF%E8%AE%A1%E7%AE%97)
2/11*13+2/13*15+2/15*17+2/17*19+2/19简便计算
2/11*13+2/13*15+2/15*17+2/17*19+2/19简便计算
2/11*13+2/13*15+2/15*17+2/17*19+2/19简便计算
2/11*13+2/13*15+2/15*17+2/17*19+2/19
=1/11-1/13+1/13-1/15+1/15-1/17+1/17-1/19+2/19
=1/11+1/19
=2/209
2/11*13+2/13*15+2/15*17+2/17*19+2/19*21+2/21
=(1/11)-(1/13)+(1/13)-(1/15)+(1/15)-(1/17)+(1/17)-(1/19)+(1/19)-(1/21)+(2/21)
=(1/11)+(1/21)
=32/231
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