关于高等数学中的逻辑证明

逻辑证明在高等数学及其教学中占有重要地位，本着重从间接证明尤其是反证法的逻辑结构入手，剖析了高等数学中的范例，反证法离不开充分条件假言推理的否定后件式，其中的后件“q”可以是直言命题或关系命题，也可以是联言命题，选言命题，假言命题和负命题。     

反证法的逻辑原理

在数学教学中,学生用“冒牌反证法”证题是屡见不鲜的。究其根本原因,是未能系统地理解反证法的逻辑原理。或者说,是未能系统地认识和掌握反证法的各种形式结构。本文以逻辑代数的基本理论,系统地论证了假言命题     

反证法在多项式理论中的应用

表达一个判断的语句称为命题,命题是由题设和题断构成。证明一个命题成立,有直接证法和间接证法。反证法属于间接证法。一般来说,大多数命题的证明是由直接证法给出的,但是当直接证法不易证明甚至无法证明时,运用反证法,有时可以收到证明既简练又确切的良好效果。因此反证法是一种重要的证明方法。然而多年来,一些人有片面的认识,认为反     

反证法的逻辑根据及其应用

反证法作为一种重要的数学方法,一般的教材都会把这个方法的步骤叙述清楚.例如,苏教版教材选修2-2[1]"间接证明"一节中指出:反证法的证明过程可以概括为"否定—推理—否定",即从否定结论开始,经过正确的推理,导致逻辑矛盾,从而达到新的否定(即肯定原命题)的过程     

反证法略谈

反证法在初等数学中不但得到广泛应用,就是在高等数学中也是不可缺少的一种重要论证方法。所以,只有搞清理论、弄清实质,学生方能掌握方法、灵活运用。但在中学阶段,学生对反证法的论证基础与反证法的逻辑原理不明,致使在证题中只能依样画瓢、机械套用。有时甚至连自己所得证明也怀疑起来,也就难怪学生在解题中尽量回避。甚至该用而不敢用。本文想就反证法的论证基础与反证法的逻辑原理等问题,谈谈个人的一些粗线看法。     

从反证法的渊源透视反证法教学难问题

反证法是数学中,尤其是高等数学中常用的一种证明方法.它是与直接证法相对的间接证法的一种.由于逻辑学中也存在同样的相关概念,所以分清反证法、归谬法以及反驳和证明之间的细微差别和联系很有必要.本文试图讲清这些概念,并指出反证法不但是最重要的证明方法,而且同其它的证明方法一样也是进行知识积累和科学发现的源泉.     

反证法就是证原命题的逆否命题吗

读了“谈数学中反证法的应用”一文，觉得部分老师对反证法的认识存在误区，虽然平时都在用反证法，但对这种证法的逻辑等价式却一知半解．文中写道：“要证命题‘若A则B’正确（简记为A→B），途径之一是证与其等价的逆否命题（简记为B→A）正确．即从否定B出发，作出一系列正确、严密、合乎逻辑的推理，最后推出与A矛盾的结论，即原命题得证．用反证法证明命题成立的基本步骤可以简单地概括为‘否定——推理一反驳——肯定’四个步骤”．     

应用反证法几例

<正>反证法是数学中一种很重要的间接证明问题的方法,一些难于从正面证明的问题,利用反证法往往能够很简明地得到解决.它的基本原理是先否定命题的结论,然后运用逻辑推理的方法推导出矛盾的结果,从而证明原命题的正确.同学们对运用反证法证题感到困难,     

反证法

所谓反证法 ,就是先假设命题的结论不成立 ,从结论的反面入手 ,进行正确的逻辑推理 ,导致结果与已知或学过的公理、定理相矛盾 ,从而得出结论的反面不成立 ,于是原结论成立 .反证法证明命题的一般步骤是 :(1)反设 :将结论的反面作为假设 ;(2 )归谬 :由“反设”出发 ,利用已知及已学过的公理、定理 ,推出与已知矛盾的结果 ;(3 )结论 :由矛盾断定“反设”错误 ,从而肯定命题的结论正确 .反证法适用于证明否定性命题、唯一性命题、“至少”、“至多”命题和某些逆命题等 .一般地说 ,凡是直接证法很难证明的命题都可考虑用反证法 .图 1例 1已知…     

重视运用反证法

<正>同学们知道,反证法是数学中的重要证明方法.牛顿曾说过:"反证法是数学家最精妙的武器之一."但不少同学由于对反证法的重要性认识不足,运用反证法的意识不强,就是偶尔使用反证法证明一个命题也经常出现失误.本文拟就反证法的运用提出几点建议.一、增强运用意识由于反证法不是现行高考的考查重点,再加上反证法推理论证方式的独特性,很多同学     

The student experience of mathematical proof at university level

While proofs are central to university level mathematics courses, research indicates that some students may complete their degrees with an incomplete picture of what constitutes a proof and how proofs are developed. The paper sets out to review what is known of the student experience of mathematical proof at university level. In particular, some evidence is presented of the conceptions of mathematical proof that recent mathematics graduates bring to their postgraduate course to teach high school mathematics. Such evidence suggests that while the least well-qualified graduates may have the poorest grasp of mathematical proof, the most highly qualified may not necessarily have the richest form of subject matter knowledge needed for the most effective teaching. Some indication of the likely causes of this incomplete student perspective on proof are presented.     

矩阵Frobenius范数不等式

1 引言与引理 矩阵范数与矩阵奇异值问题是数值代数的重要课题,并在矩阵扰动分析,数值计算等分支中起着重要作用.国内外学者对此已作了大量研究.     

由一道高考数学题来看中学数学与大学数学衔接问题

高考是高等学校选拔人才的重要手段．高考命题不仅引导着中学教学的方向,而且对高等教育也具有一定的启示作用．本文通过一道安徽省高考数学试题的解答情况,简要分析了中学当前数学教学中存在的问题,并指出大学数学与之衔接应注意的几个方面,以期为高校培养创新型人才提供一定的思路．     

Preservice Teacher Beliefs About Proofs

This article describes a study of backgrounds, beliefs, and attitudes of teachers about proofs. Thirty preservice elementary teachers enrolled in a mathematics content course and 21 secondary mathematics teachers in an abstract algebra course were surveyed. The study explored four issues: preservice teachers' experiences/exposure to proof, their beliefs about what constitutes a proof and the role of proof in mathematics, and their beliefs about when proof should be introduced in grades K-12. Results of the survey are described as a means for discussing the backgrounds and beliefs future teachers hold with regard to teaching proofs in their own classrooms. Finally, a short collection of sample explorations and questions, which could be used to encourage the thinking and writing of proofs in grades K-12, is provided. One of these questions was posed to 215 secondary students; examples of their reasoning and a discussion of the various techniques employed by the students are included.     

Mathematics teaching is democratic education

It is a commonly held belief that mathematics teaching has no political effects. Astonishingly, however, the fact is that the style of argument now used in mathematics everywhere was not developed originally to do mathematics. Originally its function was to counteract the teaching by the early Greek sophists of rhetoric. Their training gave the rich and privileged such an advantage in public speaking that democracy was threatned. Making respectable a new form of argument, in which evidence and logical structure predominated, was a very radical act of enlightened democratic education. Mathematics teaching in the form of open critical dialogue between teacher and taught remains a powerful form of education in democratic attitudes. Ambitions to produce political ideas as infallible as mathematics have a modern origin. In the early part of this century, mathematics education was again becoming universal throughout Europe. In the same period the belief arose that mathematics could eventually be completed as a single structure of truth. This transformed mathematics into a paradigm of democracy in which unorthodoxy must necessarily be eliminated. Communicated to people everywhere by universal education, this belief increased respect for similar political ideas. Gödel’s proof that mathematics can never be completed came too late to correct these political effects, but modern teachers can again use mathematics as a proof of the value and success of democratic attitudes and ideas. Whilst mathematics itself is ethically neutral, the ethical principles which produced both democracy and mathematics and which can be converyed in mathematics teaching are highly relevant to the modern world, and should be understood and taught by teachers everywhere.     

Investigating undergraduate students’ proof schemes and perspectives about combinatorial proof

Combinatorics is an area of mathematics with accessible, rich problems and applications in a variety of fields. Combinatorial proof is an important topic within combinatorics that has received relatively little attention within the mathematics education community, and there is much to investigate about how students reason about and engage with combinatorial proof. In this paper, we use Harel and Sowder’s (1998) proof schemes to investigate ways that students may characterize combinatorial proofs as different from other types of proof. We gave five upper-division mathematics students combinatorial-proof tasks and asked them to reflect on their activity and combinatorial proof more generally. We found that the students used several of Harel and Sowder’s proof schemes to characterize combinatorial proof, and we discuss whether and how other proof schemes may emerge for students engaging in combinatorial proof. We conclude by discussing implications and avenues for future research.     

A Note on Semiconcave Function

This article gives a simple proof of an equivalent proposition on semiconcave function (see [L.C. Evans (1998). Partial Differential Equations. American Mathematical Society; p. 130]). The proof of sufficiency of the proposition can be easily obtained. We prove its necessity by three steps: First, we prove that the equivalent proposition holds for discrete points <artwork name="GAPA31045ei1">; Secondly, we obtain continuity of semiconcave function; Finally, by using the fact that the sequences λ_m ^k are dense in the interval (0, 1), we prove that the equivalent proposition holds for each λ ∈ (0, 1).     

A survey of mathematics undergraduates' interaction with proof: some implications for mathematics education

Proving is an essential activity in mathematics but there are serious difficulties encountered by mathematics undergraduates in engaging with proof in the intended way. This article presents an initial analysis of (i) a quantitative study of a large sample of UK mathematics undergraduates which describes their declared perceptions about proof, and (ii) a qualitative study of a subsample of these students which analyses their actual proof perceptions as well as their actual proof practices. A comparison is also made between their publicly declared perceptions of proof and their personal proclivities in proving.     

The State of Proof in Finnish and Swedish Mathematics Textbooks—Capturing Differences in Approaches to Upper-Secondary Integral Calculus

Students’ difficulties with proof, scholars’ calls for proof to be a consistent part of K-12 mathematics, and the extensive use of textbooks in mathematics classrooms motivate investigations on how proof-related items are addressed in mathematics textbooks. We contribute to textbook research by focusing on opportunities to learn proof-related reasoning in integral calculus, a key subject in transitioning from secondary to tertiary education. We analyze expository sections and nearly 2000 students’ exercises in the four most frequently used Finnish and Swedish textbook series. Results indicate that Finnish textbooks offer more opportunities for learning proof than do Swedish textbooks. Proofs are also more visible in Finnish textbooks than in Swedish materials, but the tasks in the latter reflect a higher variation in nature of proof-related reasoning. Our results are compared with methodologically similar U.S. studies. Consequences for learning and transition to university mathematics, as well as directions for future research, are discussed.