共查询到20条相似文献，搜索用时 15 毫秒
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正一、利用公式C0n+C1n+C2n+C3n+…+Cn n=2n求和1.直接利用公式例1求和C1n+C3n+C5n+…解由于奇数项之和与偶数项之和相等,因此奇数项之和等于所有项之和的一半.所以C1n+C3n+C5n+…=1/2×2n=2n-1.2.由公式Cr n=Cn-r n进行转化例2求和1+2C1n+3C2n+…+(n+1)Cn n.解设S=1+2C1n+3C2n+…+(n+1)Cn n,其倒序和为S=(n+1)Cn n+nCn-1n+…+2C1n+1.考虑到Cr n=Cn-r n(0≤r≤n),将以上两式相加得2S=(n+2)C0n+(n+2)C1n+…+(n+2)Cn n=(n+2)·2n,所以S=(n+2)·2n-1 相似文献
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密斯特拉尔 《小学生作文辅导(作文与阅读版)》2006,(12)
星xīn星xin睁zhēn着zhe眼yǎn睛jin,挂uà在zài黑hēi丝sī绒rón上sh n亮liàn晶jīn晶jīn,你nǐ们m en从cón上shàn往wǎn下xià望wàn,看kàn我wǒ可kě纯chún真zhēn?xīnxinzhēnzheyǎnjin星星睁着眼睛,嵌qiàn在zài宁nín谧mì的de天tiān空kōn闪shǎn闪shǎn亮 相似文献
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《中学生数理化(高中版)》2006,(5)
一、赋值法例1证明下列等式:(1)C0n C1n C2n … Cnn=2n;(2)C0n C2n C4n …=C1n C3n C5n …=2n-1.证明:由二项展开式知(1 x)n=C0n C1n·x C2n·x2 … Cnn·xn.(1)令x=1,则(1 1)n=C0n C1n C2n … Cnn.即C0n Cn1 C2n … Cnn=2n.(2)令x=-1,则(1-1)n=C0n-C1n Cn2-Cn3 … (-1)n·Cnn. 相似文献
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有yǒu个ɡe女nǚ孩háir儿叫jiào钱qián钱qiɑn,帮bānɡ助zhù妈mā妈mɑ缠chán线xiàn线xiɑn。线xiàn线xiɑn长chánɡ长chánɡ绕rào钱qián钱qiɑn,钱qián钱qiɑn不bù停tínɡ缠chán线xiàn线xiɑn。长chánɡ长chánɡ线xiàn线xiɑn变biàn蛋dàn蛋dɑn,蛋dàn蛋dɑn掉diào地dì直zhí转zhuàn转zhuɑn。钱qián钱qiɑn满mǎn地dì抓zhuā蛋dàn蛋dɑn,摔shuāi了le钱qián钱qiɑn跑pǎo了le蛋dàn蛋dɑn。(正常的朗读速度为12秒,你能比这快多少?)缠线线@月月… 相似文献
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《新语文学习(小学作文)》2003,(19)
HáishiSānɡjiāyàoZhānɡjiāxiānbǔqiánɡ.Zhānɡjiāyǒuzhīyánɡ,Sānɡjiāyǒudǔqiánɡ,ZhānɡjiādeyánɡzhuànɡdǎoleSānɡjiādeqiánɡ,SānɡjiādeqiánɡyāshānɡleZhānɡjiādeyánɡ,BùzhīshìZhānɡjiāyàoSānɡjiāxiānpéiyánɡ,HáishiSānɡjiāyàoZhānɡjiāxiānbǔqiánɡ.Zhānɡjiāyǒuzhīyánɡ,Sānɡjiāyǒudǔqiánɡ,ZhānɡjiādeyánɡzhuànɡdǎoleSānɡjiādeqiánɡ,SānɡjiādeqiánɡyāshānɡleZhānɡjiādeyánɡ,BùzhīshìZhānɡjiāyàoSānɡ… 相似文献
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不等式的证明是中学数学的一个难点,通常利用数学归纳法.现介绍一种较简捷方法,即构造数列,利用数列的单调性给予证明.请看以下几例.例1对于大于1的自然数n,求证:3521212422n nnn∈,则An+1=32?5422n n??12?2n2n+1?n1+1.∴12121nnA n nA n n+=+?+22441144n nn n=+++>,∴An+1>An,∴{An}是单调递增数列.∴An≥A2=23?12=89>1,∴35212422n nn???>.设35211(1,)n242221B nn n Nn n=?????>∈,则Bn+1=23?5422n n??12?2n2n+1?2n1+1.∴21221214112214nnB n n nB n nn+=+?+?=?<,∴Bn+1相似文献
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罗艳萍 《读与写:教育教学刊》2008,5(6)
The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity. 相似文献
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Richard Denner 《海外英语》2007,(4):14-15
Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose. 相似文献
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Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F. 相似文献
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邱崇丙 《唐山师范学院学报》2014,(1):21-23
汉字的六书,《说文》对“转注”一类,语焉不详。后世学者提及转注,也仅限于许慎所举出的例字。《汉字例说》一文,作者从转注的角度综合考虑,对部分现代常用字作了分析,跟传统的解释有所不同。希望能抛砖引玉,互相切磋,以推进学术研究。 相似文献
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陈美曦 《山东教育学院学报》2008,23(2):103-107
Different nations have different social cultures, and the social culture of every nation is developing with the development of the nation, language is greatly influenced by social culture, which enables language to possess national and historical characteristics. Word is the smallest, independent, meaningful linguistic unit of language. It can well reflect the national and historical characteristics. From synchronic aspect, the social and cultural influence on word meaning is mainly embodied in conceptual and associative meanings of word. The incorrespondence of word meaning is a phenomenon that exists in both conceptual and associative meanings of word among different languages. From diachronic aspect, the development of social culture causes some changes of word meaning to some extent. Therefore, social culture plays a key role in vocabulary learning and mastery of a language. 相似文献
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Rachel Zupek 《海外英语》2007,(11):40-41
我们绝大部分人都同意一件事情——我们喜欢金钱。但是你对金钱的喜欢之情足够到让你创立一份事业么?.财富通常被人忽视,主要在于人们不能真正了 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
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Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献