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2008-06-01 11:14 来自版块 -
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teacher2:
解答:设等比数列的公比为q,等差数列的公差为d,首相为a
Cn=anbn
∑=C1+C2+……+Cn=a1b1+a2b2+……+anbn
因为qCn=an(q*bn)=anb(n+1)
所以q∑=qC1+qC2+……+qCn=a1b2+a2b3+……+anb(n+1)
...(2008-06-02 21:13)
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Itachi:
将式子乘以公比后,一般和原式作差即可。之后将所得式整一下。ok!(2008-06-01 12:33)
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