1\(19*21)+1\(21*23)+1\(23*25)+...+1\(97*99)简便,
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![1\(19*21)+1\(21*23)+1\(23*25)+...+1\(97*99)简便,](/uploads/image/z/135450-18-0.jpg?t=1%5C%2819%2A21%29%2B1%5C%2821%2A23%29%2B1%5C%2823%2A25%29%2B...%2B1%5C%2897%2A99%29%E7%AE%80%E4%BE%BF%2C)
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1\(19*21)+1\(21*23)+1\(23*25)+...+1\(97*99)简便,
1\(19*21)+1\(21*23)+1\(23*25)+...+1\(97*99)
简便,
1\(19*21)+1\(21*23)+1\(23*25)+...+1\(97*99)简便,
1\(19*21)+1\(21*23)+1\(23*25)+...+1\(97*99)
=1/2[(1/19-1/21)+(1/21-1/23)+...+(1/97-1/99)]
=1/2(1/19-1/99)
=40/1881
1\(19*21)+1\(21*23)+1\(23*25)+...+1\(97*99)
=1/2(1/19-1/21)+1/2(1/21-1/23)+...+1/2(1/97-1/99)
=1/2(1/19-1/21+1/21-1/23+...+1/97-1/99)
=1/2(1/19-1/99)
=40/19*99
原式=1/2(1/19-1/21+...-1/99)=1/2(1/19-1/99)我手机上的没草稿纸 麻烦你自己通下分嘛