圆锥曲线切线的一个统一性质

在直线和圆锥曲线的位置关系中，相切是一种重要的情况．圆锥曲线有这样一个有意思的性质：经过圆锥曲线的准线与对称轴的交点作圆锥曲线的切线，则切线的斜率的绝对值等于离心率．     

对人教版新教材一道习题的探究与拓展

本文对动圆与两定圆相切、动圆过定点且与定圆相切、动圆与定圆及定直线相切时,动圆心的轨迹作了较为全面的探究,发现其轨迹类型都是直线或圆锥曲线,探究过程多次运用圆锥曲线定义、数形结合和分类讨论的方法．     

相交时难 切也难——关于直线与圆锥曲线相切问题的系统整理及拓展研究

正圆锥曲线是优美的,因为它本身就有着近乎完美的图象;圆锥曲线是简洁的,因为它有着如此和谐的方程;圆锥曲线是重要的,因为它几乎占据了高中解析几何的全部.正因为圆锥曲线是如此优美、简洁和重要,因此教师、学者、专家对圆锥曲线的研究已经非常到位,特别是当圆锥曲线与直线相交时,被挖掘的性质、定理可以说是不计其数.当然,当直线与圆锥曲线相切时的结论也有很多,但对比相交时的情况,直线与圆锥曲线相切时的结论     

直线与圆锥曲线解题方法探究

解析几何一直是高考的热点,而其中直线与圆锥曲线的题型则贯穿了初中至高中的大小考试中,可谓是十分重要.下面,笔者总结直线与圆锥曲线的典型题型.一、直线与双曲线的位置关系直线与圆锥曲线的位置关系有三种:相交、相切、相离.当直线与双曲线相交:直线与双曲线有两个交点或有一个公共点(直线与渐近线平行);相切:直线与双曲线有且只有一个公共点,且直线不平行     

直线与有心圆锥曲线相切的一个充要条件与应用

直线与圆锥曲线的位置关系问题,涉及的知识面广,需要较强的分析综合、演绎推理能力,本文介绍直线与有心圆锥曲线相切的一个充要条件及在解题中的应用。     

关于圆锥曲线切线问题的探讨

本文从另一个角度，对过平面内任意一点与圆锥曲线相切的直线的条数做了系统的讨论，得出了圆满的结论。     

关于圆锥曲线几个问题的探讨

圆锥曲线是平面解析几何研究的主要对象。如果把圆锥曲线定义中的关键词“和（或差）”换为“平方和（或平方差）”，那么动点的轨迹或者仍然是圆锥曲线，或者是直线；一条直线，只要不与抛物线的对称轴及双曲线的渐近线平行，那么它与圆锥曲线相切的充要条件是它们只有一个公共点。这是圆锥曲线有别于其它二次曲线的一个重要特征；圆锥曲线也有类似于平面几何中切割线定理的表达式，这些表达式揭示了圆锥曲线上任意一点与共对称轴上特殊点之间的一种特殊关系。了解上述三个结论，对于进一步研究圆锥曲线的性质是十分有益的。     

抛物线的切线及其性质初探

中学教材中比较透彻地研究了直线与圆相切问题,对于直线与其他曲线,特别是圆锥曲线相切的问题教材并未介绍,但这并不意味着高中学生对这个问题没有解决办法,特别是在引进了导数这一工具性知识后,     

直线与圆锥曲线

直线与圆锥曲线的位置关系有相交、相切、相离三种,直线与圆锥曲线有两个公共点,截得的线段叫做圆锥曲线的弦.判定给定直线与圆锥曲线的位置关系一般可以通过联立其方程,推出一元二次方程,利用判别式来进行判断.直线与圆锥曲线的综合问题是历年来高考中的重要且常见的问题,这样的问题涉及的概念、知识、方法比较多,运算较繁,解题过程中一定要耐心细致,考虑全面,提高运算技能.     

对《圆与圆锥曲线的不解之缘》一文的商榷与补充

《圆与圆锥曲线的不解之缘》一文介绍了与具有不同位置关系的两个定圆都相切的动圆的圆心轨迹随两圆位置的变化而变化,但是,当两定圆相交时,动圆与两相交定圆同时相切的位置关系应该有三种情况:与两相交定圆同时外切;与两相交定圆同时内切;与两相交定圆中的一个内切,一个外切.动圆的圆心轨迹是双曲线(特殊情况是直线)或椭圆.同时,该文标题是圆与圆锥曲线的不解之缘,为了体现圆锥曲线的"完整性",本文补充了与定直线和定圆都相切的动圆的圆心轨迹是抛物线.这样我们就可以说双曲线、椭圆、圆、抛物线都能够从圆相切而生成.     

影响物流中心选址的因素及一种选址方法

文章论述了影响物流中心选址的七大因素,建议采用模糊评判的方法,该方法克服了传统选址方法的片面性、局限性和计算的复杂性,可对多种可供选择的方案做出明确的排序,使选址问题变得更加合理、科学与全面,更加反映客观实际.     

对公推直选乡镇长与乡镇党委书记的比较

公推直选乡镇长与乡镇党委书记出现的时间、发展现状与趋势、制度依据、选举成本,以及乡镇长与乡镇党委书记在乡镇政权中的作用有明显的不同。在我们看来,直接选举乡镇党委书记,发展的空间更广阔,对乡镇民主建设与乡镇政府职能转型所起的作用更大。     

Regulation and socio-emotional interactions in a positive and a negative group climate

Collaboration in an online environment can be a socially and emotionally demanding task. It requires group members to engage in a great deal of regulation, where favourable emotions need to be sustained for the group’s productive functioning. The purpose of this cross-case analysis was to examine the interplay of two groups’ regulatory processes, regulatory modes, and socio-emotional interactions that contribute to or are influenced by emotions and socio-emotional climate perceived in the group. Specifically, this study compared a group of 4 students unanimously reporting a positive climate to a group of 4 students unanimously reporting a negative climate after completing a 90-min online text-based collaborative assignment. By drawing on two data channels (i.e., observed regulatory actions and socio-emotional interactions during collaboration and self-reported data about emotional beliefs and perceptions), four contrasting group features emerged: (a) incoming conditions served as a foundation for creating a positive collaborative experience, (b) regulation of emotions during initial planning, (c) negative emotions served as a constraint for shared adaptation in the face of a challenge, and (d) encouragement and motivational statements served as effective strategies for creating a positive climate. Implications for researching and supporting emotion regulation in collaborative learning are discussed.     

Timescales and ethnography: understanding a child's meaning-making across three sites,a home,a classroom and a family literacy class

This article describes a multi-sited ethnographic study of a Turkish child, Fatih, and his mother, Elif, over a period of three years. The study was a longitudinal ethnographic project that focused on children's multimodal texts in the home. Additional research was also carried out in the classroom. This article describes the researcher's developing understanding of the meanings of Fatih's texts, and considers how the use of time scales in ethnographic work can aid understandings of texts.     

装饰画与装饰性绘画之比较

从美术中构图、色彩、形象、材料这几个方面讨论了装饰画与装饰性绘画的不同,以加深对装饰性绘画与装饰画的认识,更好地区别二者。     

夹缝中求生

文章探析托妮·莫里森小说中的黑人女性形象,解读黑人世界的美与丑、善与恶、爱与恨、生与死,关注黑人女性反抗种族、性别、文化的歧视所经历的艰难坎坷,揭示了她们追寻自我及生存意义、追求平等幸福的两难困境及其根源。     

Dynamic response of a beam on a Pasternak foundation and under a moving load

The dynamic response of an infinite beam placed on a Pasternak foundation when the system was subjected to a moving load was investigated. We used the double Fourier transform and its inversion to solve the formulations of the problem. A closed form analytic solution of the beam was obtained by the theorem of residues. We selected a numerical example to illustrate the dynamic response of the beam on Pasternak and Winkler foundations, respectively. We discuss the effect of the moving load velocity on the dynamic displacement response of the beam. The maximum deflection of the beam increases slightly with increased load velocity but increases significantly with reduced shear modulus of subgrade at a given velocity. The maximum deflection of a beam resting on a Pasternak foundation is much smaller than that of a beam on a Winkler foundation.     

论和谐社会与民主社会的关系及其构建

和谐社会首先是民主社会,民主社会是和谐社会的前提条件,和谐社会是民主社会的高级阶段。二者的这一关系决定了构建和谐社会也需要分阶段进行,首先要建设一般意义上的民主社会,实现社会的基本和谐;再建设高级阶段的民主社会——和谐社会。正确认识和谐社会与民主社会的关系对我国构建和谐社会意义重大。能为和谐社会的构建指明方向。     

Between a rock and a hard place: women and computer technology

This paper explores certain possible reasons behind the uneasy relationship between women and technology. The cultural identification of technology with masculinity has been well documented through previous research. However, we feel it is useful to revisit this complex relationship through the scope of a more subtle distinction between ‘users’ and ‘connoisseurs’, and the struggle over power, which revolves around a specific form of hegemonic masculinity. We draw on interviews that examine students’ experiences, emotions, and statements about gender, technology, mathematics, and education, and we try to offer an understanding of the ways women negotiate their position within the dominant discourse about computing and mathematics. Our analysis employs post-structuralist discourse theory.     

学科建设与专业建设的竞争与协作关系

在不同学科与不同专业之间,学科建设与专业建设两者既是相互竞争的关系,又是相互协作的关系.竞争是学科与专业建设个体性的凸现,协作是学科与专业建设系统内在的必然要求,通过竞争与合作的结合,推动学科、专业建设系统的演化和发展.