由等比数列的性质可得,S10,S20-S10,S30-S20成等比数列
∴(S20-S10)2=S10•(S30-S20)
∴400=10(S30-30)
∴S30=70
故答案为:70
设Sn是等比数列的前n项和,若S10=10,S20=30,则S30=_.
设Sn是等比数列的前n项和,若S10=10,S20=30,则S30=______.
数学人气:398 ℃时间:2019-10-24 03:22:11
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