2*{1/(2*5)}+4*{1/(5*8)}+6*{1/(8*11)}+.+100*{1/(149*152)}+102*{1/(152*155)}=?给出步骤,谢谢
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![2*{1/(2*5)}+4*{1/(5*8)}+6*{1/(8*11)}+.+100*{1/(149*152)}+102*{1/(152*155)}=?给出步骤,谢谢](/uploads/image/z/2736589-13-9.jpg?t=2%2A%7B1%2F%282%2A5%29%7D%2B4%2A%7B1%2F%285%2A8%29%7D%2B6%2A%7B1%2F%288%2A11%29%7D%2B.%2B100%2A%7B1%2F%28149%2A152%29%7D%2B102%2A%7B1%2F%28152%2A155%29%7D%3D%3F%E7%BB%99%E5%87%BA%E6%AD%A5%E9%AA%A4%EF%BC%8C%E8%B0%A2%E8%B0%A2)
2*{1/(2*5)}+4*{1/(5*8)}+6*{1/(8*11)}+.+100*{1/(149*152)}+102*{1/(152*155)}=?给出步骤,谢谢
2*{1/(2*5)}+4*{1/(5*8)}+6*{1/(8*11)}+.+100*{1/(149*152)}+102*{1/(152*155)}=?
给出步骤,谢谢
2*{1/(2*5)}+4*{1/(5*8)}+6*{1/(8*11)}+.+100*{1/(149*152)}+102*{1/(152*155)}=?给出步骤,谢谢
设n1=1/(2×5)=1/3(1/2-1/5)
n2=1/(5×8)=1/3(1/5-1/8)
……
n51=1/(152×155)=1/3(1/152-1/155)
则,n1+n2+n3+n4+……+n51=1/3(1/2-1/155)
n2+n3+n4+……+n51=1/3(1/5-1/155)
n3+n4+……+n51=1/3(1/8-1/155)
……
n50+n51=1/3(1/149-1/155)
n51=1/3(1/152-1/155)
原式=2×(n1+n2+n3+n4+……+n51)+2×(n2+n3+n4+……+n51)+2×(n3+n4+……+n51)+……+2×(n50+n51)+2×n51
=(2/3)×[(1/2-1/155)+(1/5-1/155)+(1/8-1/155)+……+(1/152-1/155)]
=(2/3)×[(1/2+1/5+1/8+……+1/152)-51/155]
只能求到这一步了,小括号内的1/2+1/5+1/8+……+1/152既非等差数列亦非等比数列,不能用现成公式精确求出.