共查询到20条相似文献，搜索用时 93 毫秒
1.
张俊英 《中学数学研究(江西师大)》2008,(5):43-44
线段的定比分点坐标公式x=(x_1 λx_2)/(1 λ),y:(y_1 λy_2)/(1 λ),λ=(x-x_1)/(x_2-x)反映了线段的起点P(x_1,y_1)、终点P_2(x_2,y_2)、分点P(x,y)与定 相似文献
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《中学数学教学参考》2007,(23)
定义若圆上任一点到点 A 的距离与到点 B 的距离的比恒为常数λ(λ>0,λ≠1),则称该圆分有向线段()所成的比是λ;该圆称为有向线段()的定比分圆.定理设 A(x_1,y_1)、B(x_2,y_2)是定点,一个圆分有向线段()所成的比是λ,则该圆的圆心坐标是 x_0=(x_1-λ~2x_2)/(1-λ~2),y_0=(y_1-λ~2y_2)/(1-λ~2),半径是 r=λ|1-λ~2|·|AB|.证明:设 P(x,y)是圆上的动点,由 |PA|/|PB|=λ得(x-x_1)~2 (y-y_1)~2=λ~2[(x-x_2)~2 (y-y_2)~2],经整理,得x~2 y~2-2x·(x_1-λ~2x_2)/(1-λ~2)-2x·(y_1-λ~2y_2)/(1-λ~2)=(λ~2x_2~2 λ~2y_2~2-x_1~2-y_1~2)/(1-λ~2),配方并化简整理,得 相似文献
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胡芳举 《中学数学教学参考》2006,(11)
笔者最近得到了二次曲线的一组统一性质,现介绍如下,供读者参考.定理1 点 N(x_0,y_0)不在二次曲线 ax~2+by~2=1上,过 N 任作一直线,交曲线于 A、B 两点,交直线l:ax_0x+by_0y=1于点 M(异于点 A、B),设=λ_1,=λ_2,则λ_1+λ_2=0.证明:如图,设点 A(x_1,y_1)、M(m,n).由条件=λ_1知点 A 分向量所成的比为λ_1. 相似文献
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《中学数学教学参考》2007,(17)
从平面几何到代数、立体几何和解析几何,证明三点共线的命题、方法、技巧,实在不少,它们都可以归结为等价命题.(1)P、Q、R 三点共线(在同一条直线上).(2)P 在直线 QR 上.(3)P 到直线 QR 的距离为0.(4)P、Q、R 都是平面α与β的公共点.(5)P、Q、R 是△ABC 外接圆上一点分别在直线AB、BC、CA 上的射影.(6)S_(△PQR)=0。(7)三点 P、Q、R 在直线 AB 同侧,且 S_(△PAB)=S_(△QAB)=S_(△RAB).(8)线段 PQ、QR、PR 中,有两条之和等于第三条.(9)k_(PQ)=k_(PR).(10)若直线 PQ 的方程为 Ax By C=0,则直线 PR 的方程为 kAx kBy kC=0(k≠0为常数).若设三点 P、Q、R 的坐标分别为(x_1,y_1)、(x_2,y_2)、(x_3,y_3),则有(11)(x_3,y_3)满足方程(x-x_1)/(x_2-x_1)=(y-y_1)/(y_2-y_1).(12)设λ_1=(x_1-x_2)/(x_2-x_3),λ_2=(y_1-y_2)/(y_2-y_3),则λ_1=λ_2. 相似文献
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《中学生数理化(高中版)》2007,(5)
设P_1、P_2是直线l上的两点,点P是l上不同于P_1、P_2的任意一点,则存在一个实数λ,使(?)=λ(?),λ叫做点P分有向线段(?)所成的比,记为λ=(?).若P_1(x_1,y_1)、P_2(x_2,y_2)、 相似文献
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叶芳琴 《中学数学教学参考》1995,(5)
我们知道,在直角坐标系中,设点P_1(x_1,y_1)、P_2(x_2,y_2),若点P(x,y)为有向线段P_1P_2的内(外)分点,则点P分P_1P_2所成的比λ为 λ=(P_1P)/(PP_2)=(x-x_1)/(x_2-x)(=(y-y_1)/(y_2-y)>0(<0)。 (*) 特别地,当线段P_1P_2落在x轴上时,纵坐标为0,情形就更加明了(以下讨论仅在x轴上进行,且不妨约定x_10(λ<0),则P为P_1P_2的内(外)分点,亦即P点介于P_1P_2之间(之外),这时有x_1相似文献
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考虑到定比分点公式中λ是有向线段的比,我们可以很容易地得到一个很有用处的定理:过 P_1(x_1,y_1),P_2(x_2,y_2)两点的直线若与直线L:Ax+By+C=0相交于点P,则 相似文献
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有向线段(其中P_1(x_1,y_1),P_2(x_2,y_2))的定分点坐标公式是,这是一个结构整齐,对称,数学美感强的公式,当且仅当λ>0时,分点位于p_1,p_2之间;当且仅当λ<0且λ≠-1时,分点位于的延长线上或反向延长线上,或者退缩为一点。 相似文献
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张威 《中国教育研究与创新》2006,3(11):145-150
天保房地产开发公司根植于天津滨海新区。依托控股公司带来的资源优势，基于滨海新区列入国家发展战略部署的背景，在近年来取得了迅速的发展。但是随着国家一系列政策的出台，中国的房地产行业面临着一次大的重新洗牌过程，同时企业内部仍然存在着制度缺陷、管理不规范、流程不清晰、人员激励不足等各方面的问题，所以，天保房地产公司在面临着滨海新区良好发展机遇的同时，也面临着很大的挑战。如何在机遇与挑战并存的环境中，认真分析和评估企业的外部环境及内部资源与能力的优劣势，对企业内部的资源与能力进行积累与培养，制定相应的竞争与发展战略，引导企业的健康长远发展具有一定的必要性与迫切性。
本文从竞争战略的角度，综合分析天保房地产开发公司所面临的外部环境和内部条件，研究探讨天保房地产开发公司的发展战略框架，包括战略的指导思想、战略定位、战略目标及相应的实施措施，以期实现天保房地产开发公司的发展愿景和核心价值。 相似文献
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The experiment in which a candle is burned inside an inverted vessel partially immersed in water has a history of more than
2,200 years, but even nowadays it is common that students and teachers relate the change in volume of the enclosed air to
its oxygen content. Contrary to what many people think, Lavoisier concluded that any change in volume in this experiment is
negligible; moreover, the explanation relating oxygen consumption in the air with its change in volume is known to be wrong.
In this work we briefly review the history behind the candle experiment and its relationship with some typical erroneous explanations.
One of the key factors behind Lavoisier’s success was the use of experiments carefully designed to test different hypotheses.
Following these steps, we performed several closed volume experiments where the candle wick was replaced by a capillary stainless
steel cylinder supported and heated by a nichrome filament connected to an external power supply. Our recorded experiments
are displayed as web pages, designed with the purpose that the reader can easily visualize and analyze modern versions of
Lavoisier’s experiments. These experiments clearly show an initial phase of complete combustion, followed by a phase of incomplete
combustion with elemental carbon or soot rising to the top of the vessel, and a final phase where the hot artificial wick
only evaporates a white steam of wax that cannot ignite because no oxygen is left in the closed atmosphere. After either a
complete or incomplete combustion of the oxygen, our experiments show that the final gas volume is nearly equal to the initial
air volume. 相似文献
13.
徐振芳 《中学英语之友(高二版)》2008,(Z2)
秦二世时,丞相赵高野心勃勃,日夜盘算着要篡夺皇位。可朝中大臣有多少人能听他摆布,有多少人反对他,他心中没底。于是,他想了一个办法,准备试一试自己的威信,同时也可以摸清敢于反对他的人。 相似文献
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Easy Phonics带你学习自然拼读,让你学会字母的发音规律,正确地拼读单词。本期让我们继续来看看、读读、写写重读音节中包含字母a的单词,区分它们读短音short a-/e/,还是长音long a-/ei/。 相似文献
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Easy Phonics栏目带你轻松地学习自然拼读!在读读、听听、拼拼和玩游戏中,你将了解字母的发音规律,并正确地拼读单词。这一期,我们来学习元音字母a的短音(short a)和长音(long a). 相似文献
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从前,有一句话,叫做"吃得苦中苦,方为人上人".这句话被认为动机不纯,怎么可以做"人上人"呢?其实,对于"人上人"可以作不同的理解,一种理解是"骑在人民头上,作威作福",这种"人上人"当然不好;但也可以解释为比别人做更多的贡献,吃更多的苦,经过更多的挫折与困难而比一般人更成熟、更坚强,更知道怎么做人.实际上,对这句话应是作后一种理解的,因为这种"人上人"是与"苦中苦"联系在一起的. 相似文献
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张昭兵 《南京师范大学文学院学报》2009,(4):37-44
本文从毕飞宇小说中一再出现的镜、钟、影和胡琴的意向入手,考察毕飞宇小说的叙述人称、叙述速度、叙述结构和叙述意图。深入阐释＂我＂与＂他＂的分离与揉合,＂快＂与＂慢＂的交替与演变,＂是＂与＂非＂的分明与模糊,＂语言＂与＂沉默＂的相反而相成。 相似文献
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The concept of metacognition refers to one’s knowledge and control of one’s own cognitive system. However, despite being widely
used, this concept is confusing because of several reasons. First, sometimes it is not at all clear what is cognitive and
what is metacognitive. Second, researchers often use the same term, namely, “metacognition” even when they refer to very different
aspects of this complex concept. Alternatively, researchers may use different terms to indicate the same metacognitive elements.
Another foggy matter is the interrelationships among the various components of metacognition discussed in the literature.
This conceptual confusion regarding the concept of metacognition and its sub-components calls for in-depth theoretical and
conceptual clarifications. The goal of this article is to portray a detailed example of a conceptual analysis of meta-strategic
knowledge (MSK) which is one specific component of metacognition. This specific example is used to draw a general model for
conceptual analyses of additional metacognitive components. The approach suggested here is to begin with a clear definition
of the target sub component of metacognition, followed by a systematic examination of this sub component according to several
dimensions that are relevant to metacognition in general and to that sub component in particular. The examination should include
an analysis of how the details of the definition of the target sub-component refer to: (a) general theoretical metacognitive
issues raised by prominent scholars; (b) definitions formulated and issues raised by other researchers who have investigated
the same (or a similar) sub-component and, (c) empirical findings pertaining to that sub-component. Finally, it should be
noted that since metacognition is a relational rather than a definite concept it is important to situate the context within
which the conceptual analysis takes place. 相似文献
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