一道美国大学生数学竞赛题的推广

利用积分形式的侯尔德不等式对美国2006年大学生数学竞赛的一道试题作出推广.     

一道竞赛题的另解

试题在△ABC中,∠A=2∠B,CD是∠ACB的平分线,求证:BC=AC+AD.该试题是2012年四川初二数学竞赛(初赛)试题,所给参考答案如下:图2如图2,将A沿CD反射到BC上得A′,则∠CA′D=∠A=2∠B=∠B+∠A′DB,故∠B=∠A′DB,AD=A′D=A′B,故BC=A′C+A′B=AC+AD.在老师的指导下,我得到了该试题的另外2种漂亮解答,如下:另解1如图3,延长BA至E使AE=AC,连结,因为     

一道竞赛题的推广

20 0 1年全国高中数学联赛题 5为 :若 (1+ｘ +ｘ2 ) 10 0 0 的展开式为ａ0 +ａ1ｘ +ａ2 ｘ2 +… +ａ2 0 0 0·ｘ2 0 0 0 ,则ａ0 +ａ3+ａ6 +ａ9+… +ａ1998的值为 (　　 )(Ａ) 3333.　　　 (Ｂ) 36 6 6 .(Ｃ) 3999. (Ｄ) 32 0 0 1.该题构思巧妙 ,解法灵活 ,可谓独具匠心 .笔者经研究发现 ,此处ａ1+ａ4 +ａ7+… +ａ1999=ａ2 +ａ5+ａ8+… +ａ2 0 0 0 =3999,因此 ,此题结论可以推广 .推广 1　设 (1+ｘ +ｘ2 ) ｎ(ｎ∈Ｎ)的展开式中 ,指数能被 3整除的项的系数和为Ａｎ,除以 3余 1的项的系数和为Ｂｎ,除以 3余 2的项的系数和为Ｃｎ,则Ａｎ=Ｂｎ=…     

一道数列竞赛题的另解

题目 已知数列{an}满足:a1=2t-3(t∈R,且t≠1),an+1=(2tn+1-3)an+2(t-1)tn-1/an+2tn-1(n∈N*).(1)求数列{an}的通项公式;(2)若t＞0,试比较an+1与an的大小.     

另解竞赛题

看了本刊2010年1月上P31《从一道智慧窗的巧解说起》,本刊7月下P29《一道竞赛题的另解》及P40《也谈一道竞赛题的解法》,感到多位作者热情关注此类赛题,各出奇招,巧妙解答,真是百花齐放,满目玲珑.本人也提供另一种解法,想让百花丛中增添一朵鲜花.     

一道竞赛题的推广

问题（第十四届“希望杯”高一第二试）若sin^3θ-COS^3θ=-1，则sinθ-cosθ的值为     

一道竞赛题的另解与推广

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一道竞赛题的推广及应用

2004年全国高中数学联赛吉林赛区初赛第四大题是:设ai∈R ,i=1,2…,5.求a1a2 3a3 5a4 7a5 a2a3 3a4 5a5 7a1 … a5a1 3a2 5a3 7a4的最小值.本文笔者将给出这道试题的一个推广及应用.命题设xi>0(i=1,2,…,n),n∈N,n≥3,数列{λn}成正项等差数列,则x1λ1x2 λ2x3 … λn-1xn x2λ     

三解一道竞赛题

题目已知α为锐角,求证：1/sinα＋3√3/cosα≥8.     

Ad Hoc网络区域划分和资源分配问题评注

简述2006年全国研究生数学建模竞赛A题的命题背景和设计思路,并对A题参赛论文所涉及的思想与方法进行评注.     

2015年全国研究生数学建模竞赛D题的赛后评述

2015年全国研究生数学建模竞赛D题是面向节能的单/多列车优化决策问题,题中包括3个问题:单列车节能运行优化控制、多列车节能运行优化控制问题、列车延误后运行优化控制问题.分别对这三个问题做一些评述.     

“军事行动避空侦察的时机和路线选择”评注

简述2016年全国研究生数学建模竞赛D题军事行动避空侦察的时机和路线选择的命题背景、数据来源和设计思路,并对参赛论文所涉及的有关问题进行评注.     

积分型Cauchy中值定理的推广及逆问题

给出了一个积分型Cauchy中值定理的推广,并讨论了连续函数的积分型Cauchy中值定理的逆问题.     

Interior variations in dynamic optimization problems

In this article, the author examines the properties of interior variations and indicates how to use them in order to formulate the necessary condition of optimality for problems of dynamic optimization, in particular, problems of variational calculus and of optimal control. For optimal control problems, an optimization technique based on interior variations and polynomial approximations is suggested and then illustrated by an explanatory example.     

Inverse Problem of the Calculus of Variations for Systems of Differential-Difference Equations of Second Order

The inverse problem of the calculus of variations for second-order nonlinear and linear systems of differential-difference equations is considered. The relationship between the formal potentiality of a linear system with constant coefficients and the parity of its characteristic function is established.     

Mimicry of proofs with computers: the case of Linear Algebra

In common teaching practice the habit of connecting mathematics classroom activities with reality is still substantially delegated to wor(l)d problems. During recent decades, a growing body of empirical research has documented that the practice of word problem solving in school mathematics does not match this idea of mathematical modelling and mathematization. If we wish to construct ‘real problems arising from real experiences of the child’ following the spirit of these new suggestions, we have to make changes. On the one hand we have to replace the type of activity in which we delegate the process of creating an interplay between reality and mathematics by substituting the word problems with an activity of realistic mathematical modelling, i.e. of both real-world based and quantitatively constrained sense-making; and, on the other hand, to ask for a change in teacher beliefs; furthermore, a directed effort to change the classroom socio-math norms will be needed. This paper discusses some classroom activities that takes these factors into account.     

On a class of logarithmic integrals

In this note we give closed forms for a class of logarithmic integrals in terms of Bernoulli polynomials. This provides a method for unifying a large class of definite integrals.