复数在几何中的应用

复数可以用点和向量表示,复数集与复平面上的点集及复平面上从坐标原点发出的向量集具有一一对应关系,复数的加减法运算可以按照向量的加减法进行,若设z=r(cosθ isinθ)复数z_1与向量OZ_1对应,那么Z·z_1的几何意义是把向量OZ_1绕o点按逆时针方向旋转θ角,再把|OZ_1|变为原来的r倍,而z-1/z(z≠0)的几何意义则是把向量OZ_1绕o点按顺时针方向转θ角,再把|OZ_1|变为原来的1/r倍,根据复数及其运算的几何意义,平面上某些图形的几何关系可以通过复数关系来刻划,从而一些几何问题就可以通过一系列的复数运算,巧妙地导出所需的结果。     

复数题的平几直观解法

应用复数的向量表示及其运算的几何意义,可以十分简捷地解决平面几何、平面解析几何以及三角中的许多问题,对此己有好多文章作了详尽的论述.本文考察其另一面,试就如何根据复数及其运算的几何意义,应用平几知识来直观地求解一些复数问题,作一粗浅的探讨,供大家参考.     

解复数高考题的整体思维策略

在解复数高考题时 ,学生往往不加思索地用复数的代数形式或三角形式求解 ,导致繁琐运算或解题思路受阻。其实 ,处理复数问题在策略上 ,若能从宏观上分析问题的结构特征和内在联系 ,整体思维 ,则可避繁就简 ,优化解法 .本文例举几种常用策略供参考 .1　整体换算策略在复数运算中 ,充分利用“ｉ”、“ｗ”的性质 ,如 ( 1±ｉ) 2 =± 2ｉ,( - 12 ± 32 ｉ) 3 =1等 ,将题中式子重新组合 ,视作一个整体 ,灵活地进行等量代换 ,可优思省算 .例 1　 ( 1 997年全国高考题 )已知复数ｚ=32 - 12 ｉ,ｗ =22 22 ｉ,复数ｚｗ ,ｚ2 ｗ3 在复数平面上所对…     

论复数在三角上的应用

根据复数的初等性质和运算法则,使我们能充分地利用复数去研究三角中的问题。例如,利用棣莫佛定理能够推出倍角的正余弦公式,利用复数的乘法和乘方法则可以推出正弦和余弦的加法定理等等。此外,利用复数可以证明三角中的一些重要公式、定理,还可以证明三角恒等式和计算三角和等问题。本文的目的是利用复数解三角中的一些问题。为了方便起见,我们给复数以简便记号,这种记号被称作Francais记号,1813年由他所创,后来被柯西采用过。     

略谈平方的“功”与“过”

平方与开方是数学解题中常用的运算之一,这种运算解决了不少问题,有时还对解题带来不少方便,但必须指出,不适当地使用平方也可能导致各种错误。下面通过具体例题,说明平方的“功”与“过”,从而在实践中合理地利用平方这个工具。例1 求实数x和y,使x~2-y~2 2xyi=8 6i。分析对这道题,一般的方法是用复数相     

复数計算与几何証題

同学們在代数課程中学习复数这一部分的时候,一般对复数的代数演算注意得比較多,而对这种数及其运算的几何意义注意得比較少。其实,复数及其运算的几何解释在数学中有着重要的地位,在物理学、力学中有着广泛的应用。在这一讲中我們要比較詳細地解释一下复数及其四則运算的几何意义,并且用一些有趣的例子来說明怎样利用复数演算来証平面几何題。一、复数的几何意义大家知道,如果我們在平面上引进一个笛卡儿坐标系,那么任何一个复数     

某些特殊三角形的复数表示

在中学代数里我们学过复数,我们知道,复数可用平面上的向量或点来表示,利用复数的基本运算及其几何意义,已经解决了许多平面几何问题.本文对此不作详细介绍,而限于讨论怎样用复数表达一个三角形     

若干复数问题的几何直观

学了复数及其运算以后,一般学生都不习惯应用它们的几何意义思考问题,这当然不利于学生对复数的几何意义的掌握,也影响他们解题能力的提高,因此在教学过程中适当地补充一些应用这方面知识的例题,有助于学生逐步地形成应用复数几何意义的意识和提高应用这方面知识的能力,下面的一些例题可供参考。例1、设z是满足|z|=1的复数,求|z-2|的范围。解:设复数z在复平面上对应的点为Z,依题设,Z位于以原点为圆心的单位圆上。从而     

复数方程表示曲线时的“同解性”问题

曲线与方程是平面解析几何的一个大题目,复数这一章也涉及到曲线与方程,但未作详细研究,本文引用一些常见的例子,对曲线与复数方程作一些探讨,并适时地提出几点应注意的问题。由于复数集与复平面所有点的集合的一一对应的关系,为了叙述上的方便,我们在本文中约定,复数     

z_1 z_2与z_1-z_2的辩证处理

复数集中,从形式上看,z_1 z_2与z_1-z_2是不同的运算,但由于负数概念的引入,“加”与“减”可以互相转化。这样z_1 z_2与z_1-Z_2实际上可以统一起来。它们的这种辩证统一,给复数运算带来极大方便。相比之下,在几何意义应用方面,z_1-z_2比z_1 z_2更优。这一方面由于|z_1-Z_2|表示了复平面内z_1、z_2两个复数对应点间的距离,另一方面复数z_1、z_2所对应的点与差z_1-Z_2所对     

On the solution of problems of filtration with a limit gradient

The plane stable filtration of an incompressible liquid with a limit gradient is considered /1/. A special non-linear filtration law is introduced, for which the basic system of equations obtained by transformation of the hodograph /2/ has a general solution which enables the theory of functions of a complex variable to be effectively employed. As a special case the proposed law contains the law considered in /3/. Solutions of the problems of the motion produced by a source in a narrow zone, and the motion from a source-sink pair are presented.     

Stabilization of the motions of mechanical systems with variable masses

A holonomic mechanical system with variable masses and cyclic coordinates is considered. Such a system can have generalized steady motions in which the positional coordinates are constant and the cyclic velocities under the action of reactive forces vary according to a given law. Sufficient Routh-Rumyantsev-type conditions for the stability of such motions are determined. The problem of stabilizing a given translational-rotational motion of a symmetric satellite in which its centre of mass moves in a circular orbit and the satellite executes rotational motion about its axis of symmetry is solved.     

昆虫振翅飞行的数值模拟

在非惯性参考系下对昆虫振翅扰动的二维非定常流场进行了数值模拟,避免了计算中的移动边界困难,从而缩短了计算时间,模型具有3个自由度,可以模拟任意已知的翅的平面运动．通过模拟相对复杂的自然界昆虫的振翅运动,研究昆虫是如何控制飞行．计算结果表明,有2个参数可能被昆虫用来控制飞行:翅平动和转动间的相位差以及垂直于平均振翅平面方向的横向振幅．     

On the dynamics of a rigid body carrying a material point

In this paper we consider a system consisting of an outer rigid body (a shell) and an inner body (a material point) which moves according to a given law along a curve rigidly attached to the body. The motion occurs in a uniform field of gravity over a fixed absolutely smooth horizontal plane. During motion the shell may collide with the plane. The coefficient of restitution for an impact is supposed to be arbitrary. We present a derivation of equations describing both the free motion of the system over the plane and the instances where collisions with the plane occur. Several special solutions to the equations of motion are found, and their stability is investigated in some cases. In the case of a dynamically symmetric body and a point moving along the symmetry axis according to an arbitrary law, a general solution to the equations of free motion of the body is found by quadratures. It generalizes the solution corresponding to the classical regular precession in Euler??s case. It is shown that the translational motion of the shell in the free flight regime exists in a general case if the material point moves relative to the body according to the law of areas.     

Modular-function representation of the solutions of the problem of two fixed centres

The problem of two fixed centres can be integrated in quadratures by using Stoeckel's theorem in spheroidal coordinates. The elliptic coordinates of the meridian plane satisfy equations that define a complex elliptic curve. The solution can be written down by using the uniformization formula of the elliptic curve. The constants defining the result in terms of doubly periodic functions are calculated successively from the initial data. The half-period ratio is determined by solving a complex transcendental equation using modular functions. The magnitude of the half-period of least absolute value is determined using -functions of the zero argument, using invariants of the Weierstrass -function.     

Two-step generation of the equations of motion of closed-chains

This paper presents a two-step generation of the equations of motion of planar mechanisms using point and joint coordinates. First, the formulation replaces a rigid body by a dynamically equivalent constrained system of particles and uses Newton’s second law to study the motion of the particles without introducing any rotational coordinates. Then, the equations of motion are transformed to a reduced set in terms of selected relative joint variables using a velocity transformation matrix. For an open-chain, this process automatically eliminates all of the non-working constraint forces and leads to an efficient integration of the equations of motion. For a closed-chain, suitable joints should be cut and few cut-joints constraint equations are included. An example of a closed-chain is used to demonstrate the generality and efficiency of the proposed method.     

The optimum rectilinear motion of a two-mass system

The forward rectilinear motion of a system of two rigid bodies along a horizontal plane is considered. Forces of dry friction act between the bodies and the plane, and the motion is controlled by internal forces of interaction between the bodies. A periodic motion in which the system moves along a straight line is constructed. The optimum parameters of the system and a control law are found corresponding to the maximum mean velocity of motion of the system as a whole.     

One-Parameter Homothetic Motion in the Hyperbolic Plane and Euler-Savary Formula

In [10] one-parameter planar motion was first introduced and the relations between absolute, relative, sliding velocities (and accelerations) in the Euclidean plane \mathbb E²{{\mathbb E}^2} were obtained. Moreover, the relations between the complex velocities of one-parameter motion in the complex plane were provided by [10]. One-parameter planar homothetic motion was defined in the complex plane, [9]. In this paper, analogous to homothetic motion in the complex plane given by [9], one-parameter planar homothetic motion is defined in the hyperbolic plane. Some characteristic properties about the velocity vectors, the acceleration vectors and the pole curves are given. Moreover, in the case of homothetic scale h identically equal to 1, the results given in [15] are obtained as a special case. In addition, three hyperbolic planes, of which two are moving and the other one is fixed, are taken into consideration and a canonical relative system for one-parameter planar hyperbolic homothetic motion is defined. Euler-Savary formula, which gives the relationship between the curvatures of trajectory curves, is obtained with the help of this relative system.     

The relative equilibria of a tethered gyrostat in a central Newtonian field

The motion of an orbital tether system comprising a massive body and a gyrostat of small mass attached to it by a non-extensible weightless tether is examined. The body performs unperturbed motion in a Kepler orbit. There are several different equilibria of the system relative to a uniformly rotating system of coordinates. These equilibria are interpreted geometrically using Mohr circles. Despite being the simplest example of an orbital tether system with a gyrostat, it exhibits a wealth of dynamic properties. There are also more complex orbital tether systems which contain more than one gyrostat [1].     

Hybrid control for tracking environmental level sets by nonholonomic robots in maze-like environments

A non-holonomic constant-speed robot travels in an unknown maze-like environment cluttered with complex obstacles. Through the obstacle-free part of the plane, the robot should autonomously arrive at the isoline where an unknown scalar field assumes a given value. Afterwards, it should track the obstacle-free part of the isoline. The robot has access only to the field value at the current location and the distance from this location to the obstacles. We present a hybrid nonlinear navigation law that solves this mission. The law does not use estimation of the field gradient and is non-demanding with respect to both computation and motion. The non-local convergence of the proposed algorithm is rigorously justified and confirmed by computer simulation tests.