新题征展(121)

A 题组新编 1.(胡寅年)(1)以一个正方体的顶点为顶点的四面体共有 A.70个B.64个C.58个D.52个 (2)以一个正方体的顶点为顶点的正四面体共有 A.2个B.8个C.16个D.24个 (3)以一个正方体的顶点为顶点的正三棱锥共有 A.8个B.10个C.16个D.24个 (4)以一个正方体的顶点为顶点的四个面都是直角三角形的三棱锥共有 A.12个B.24个C.36个D.48个 2.(胡寅年)(1)设f(x)是定义在(-∞,+∞)上的可导函数,且满足f'x+f(x)>0,对任意正实数a,下面不等式恒成立的是     

巧求概率

，.人下.‘.，.直.，.‘.，.‘.，.玉甲. 12个排球队中有两个强队，将这12个队分成两组(每组6个队)，求这两个强队被分在一个组内的概率.五，..口，.二甲.人丫-盛，.‘.，解两个强队分别简称A、B，若强队A的编组已定，则与A同组的空位有5个，与A不同组的空位有6个.将B填入这n个     

分苹果,花样多

1.中秋节这天,莫尔夫人请古拉格、嘟拉拉和谷拉拉到家里做客,并拿出5个苹果,让他们和自己的三个儿子分. 莫尔夫人:欢迎你们!这里有5个苹果,你们6个人自己平均分一分吧. 2.大宝:我们每人拿1个. 谷拉拉:不行!只有5个苹果!     

1999年小学数学奥林匹克初赛卷

(适用于五年级)(本卷时间90分钟,总分160分,每小题10分) I.计算:1999 999 99 9=——. 2.计算:丢 { 丢 { 吉= 3.计算:102 97 29 65 98 203 35 91=——. 4.计算:1999×123= . 5.在下边的乘法算式中,每个口表示一个数字,那么计算所得的乘积应是——. 2口 !,量王 8口 口口口 口口口4 6.用一个l,一个2,一个3可组成若干个不同的三位数,这些三位数一共有——个. 7.在一本数学书中,有100个插图是平行四边形,其中80个是长方形,40个是菱形,那么这本书的插图中正方形有——个 8.已知正方形.ABCD的对角线长为10厘米,则它的面积为——. 9.在方框中填人…     

一类完全平方数

先看一看下面的两个命题:1.两个相邻偶数的乘积加上1是一个完全平方数.2.四个连续整数的乘积加上1是一个完全平方数.这是两个熟知的命题,证明都是基于代数式变形中的配方.注意到,一个完全平方数减去1可以通过平方差变为两个式子的乘积,上述两个命题都是对此问题经“逆向思考”后得到的.本文就这类完全平方数介绍一些性质和结论.例1设a、6为正整数,且nb+1是完     

孙子问题及巧解

一、孙子问题《孙子算径》是我国唐初的“算学”教科书,分上、中、下三卷.其下卷第26题是一个闻名世界的数学问题.这个问题有人称为“孙子问题”.即“今有物不知其数,三三数之剩二,五五数之剩三,七七数之剩二,问物几何?”用现代话来说是:今有一堆东西.不知它的数量.如果三个三个地数最后剩二个,五个五个地数最后剩三个,七个七个地数最后剩二个.问这一堆东西有多少个?     

完全超紧图

Chia G.L.和Lim C.K.在东南亚第一次图论会议(1983,新加坡)文集的末尾提出六个未解决问题.第五个问题是:设H是自补图,问是否存在自补完全超紧图G,使G~*=H.第六个问题是:设G是完全超紧图.如果G_0与(?)同构,问G是否自补图.本文肯定地回答了第五个问题和否定地回答了第六个问题.     

妙用抽屉原理证明不等式

我们知道,3个苹果放在2个抽屉里,必然有一个抽屉里有2个苹果.这是一个简单的事实,人们称其为抽屉原理.妙用抽屉原理,证明某些不等式,能起到比较神奇的效果.本文给出几个例子.     

2006年高考数学北京卷

一、选择题:共8小题,每小题5分,共40分.1.在复平面内,复数1i+i对应的点位于A.第一象限B.第二象限C.第三象限D.第四象限2.若a与b-c都是非零向量,则“a·b=a·c”是“a⊥(b-c)”的A.充分而不必要条件B.必要而不充分条件C.充分必要条件D.既不充分也不必要条件3.在1,2,3,4,5这五个数字组成的没有重复数字的三位数中,各位数字之和为奇数的共有A.36个B.24个C.18个D.6个4.平面α的斜线AB交α于点B,过定点A的动直线l与AB垂直,且交α于点C,则动点C的轨迹是A.一条直线B.一个圆C.一个椭圆D.双曲线的一支5.已知f(x)=l(o3gaa-x,1x)≥x+14a,x<1,…     

从一道错题再谈函数图象的交点问题

文[1]中例2的题目与原作者提供的答案如下: 　　题目已知0相似文献   

Study of the blow-up of solutions of systems of equations of hydrodynamic type

Mathematical Notes - We study the initial boundary-value problem for three-dimensional systems of equations of pseudoparabolic type. The system is similar to the Oskolkov system, but differs from...     

Distribution of types of symmetry of tensors of high degree

The asymptotic distribution of tensors of degree N in symmetry types is studied in this paper.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 155, pp. 181–186, 1986.     

Characterization of types of asymptotic discernibility of families of hypotheses

We give a characterization of the types of asymptotic discernibility of families of hypotheses in the case of hypothetical measures that are not, in general, mutually absolutely continuous. The case when the logarithm of the likelihood ratio admits an asymptotic expansion of the type of an expansion with local asymptotic normality is examined in detail. Examples are studied.Translated fromTeoriya Sluchainykh Protsessov, Vol. 15, pp. 64–71, 1987.     

Axiomatizability of reducts of algebras of relations

In this paper, we prove that any subreduct of the class of representable relation algebras whose similarity type includes intersection, relation composition and converse is a non-finitely axiomatizable quasivariety and that its equational theory is not finitely based. We show the same result for subreducts of the class of representable cylindric algebras of dimension at least three whose similarity types include intersection and cylindrifications. A similar result is proved for subreducts of the class of representable sequential algebras. Received October 7, 1998; accepted in final form September 10, 1999.     

Lengths of periods of continued fractions of square roots of integers

Empirical study of the period’s length T of the continued fractions of $\sqrt{Q}$ (for growing integers Q) shows several strange asymptotical results, for instance, $T\leq C\sqrt{Q}\ln{Q}$ . These results show important differences between the statistics of the elements of the continued fractions of random real numbers and of square roots of random integers.