,求出n的值.解答: 解:(1)设等比数列{an}的首项为a1,公比为q,依题意,有2(a3+2)=a2+a4,由S4-S1=28可得a2+a3+a4=28得a3=8∴a2+a4=20 …(3分)∴ a1q+a1q3=20 a3=a1q2=8 解之得 q=2 a1=2 或 q= 1 2 a1=32 …(5分)所以 an=2n或an=( 1 2)n-6...
28 months 1ater the coronavirus pandemic as an ana1ogy for future sustainabi1ity cha11engesWe combine the concepts of `black elephants' and wicked problems with Roy Bhaskar's critical realist philosophy of science and frame the current state of the coronavirus pandemic as an analogy for ...
已知等比数列{an}的前n项和Sn满足:S4-S1=28.且a3+2是a2.a4的等差中项.(1)求数列{an}的通项公式,(2)若数列{an}为递增数列...问是否存在最小正整数n使得成立?若存在.试确定n的值.不存在说明理由.
。。líī.ì“i286000上11102』堂She N AN s2:。兰『S1N A N N N 奶NM NN 0。1H!。。 。画上客N。。N。N N C OU T SN。 『。『I3=hm tm nl m.menh.m一 相关知识点: 试题来源: 解析 【解析】 1.C 2.B 3.A 4.D 5.B 6.D 7.A 8.C 9.A 10.D 11.B 12.D 13....
等比数列{an}的前n项和为Sn,已知S1,S3,S2成等差数列. (1)求{an}的公比q; (2)若a1-a3=3,求Sn. 试题答案 在线课程 (1) (2) (1)∵S1,S3,S2成等差数列, ∴2S3=S1+S2,即2(a1+a2+a3)=a1+a1+a2,∴2a3=-a2,∴q= . (2)a3=a1q2= ...
根据最后一段中"The set of speech sounds we use has not necessarily remained stable since the appearance of human beings,but rather the huge variety of speech sounds that we find today is the product of a complex interplay of things like biological change and cultural evoluti...
妈妈再爱我一次_04,口碑佳作,电视剧剧情:该剧讲述了悲情母亲蒋安雯在丈夫变成植物人后,用真心感化继子,并带着孩子一次又一次的与命运抗争的故事。
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那座城这家人[DVD版]_05,电视剧剧情:1976年,一场7.8级地震,把王大鸣、林智燕小两口,双双埋在矿医院。六天七夜后,王大鸣获救,醒来得知:身怀六甲的妻子没了,老爸没了。左邻右舍,家家戴孝。在震后忘我工作的日子里,...
The analysis was done by analysing scenes within an episode of an American television series, `How I Met Your Mother'. Examples of politeness strategies were analysed and discussed based on Brown and Levinson's (1978, 1987) politeness strategies. The findings of this study would be useful ...