谈过任一点作三次曲线切线的条数问题

2007全国卷(Ⅱ)22题:已知函数f(x)=x3-x,(Ⅰ)求曲线y=f(x)在点M(t,f(t))处的切线方程;(Ⅱ)设a>0,如果过点N(a,b)可作曲线y=f(x)的三条切线,证明:-a相似文献   

三次曲线切线的一个结论

结论 若直线与三次曲线相切,则切点唯一. 证明 假设f(x) =ax3 +bx2 +cx+d(a≠0),直线l与三次曲线y＝f(x)有两个不同的切点T1(t1,f(t1))、T2 (t2,f(t2)),t1≠t2.则l的方程为: y-f(t1)=f'(t1)(x-t1)或 y-f(t2)=f'(t2)(x-t2), 即y=(3at21+2bt1+c)x+(-2at31-bt21+d)或y＝(3at21+2bt2 +c)x+(-2at32-bt22+d).     

微分差分方程解的有界性与稳定性

1.本文首先是讨论微分差分方程 dx(t)/dt=a(t)x(t)+b(t)x(t-1)+f(t) t_o≤t<∞(1.1)解的稳定性。方程(1.1)中的a(t),b(t)和f(t)是实变数t的实函数,我们求满足(1.1)和初始条件x(t)=g_1(t),t_o-1≤t≤t_o的解,此处9_1(t)是预给的函数。其次是研究二階差分方程和     

谈过任一点作三次曲线切线的条数问题

2007全国卷（Ⅱ）22题：已知函数f（x）=x^3-x。（I）求曲线y=f（x）在点M（t，f（t））处的切线方程；     

一道高考题的推广、类比拓展与证明

以下是2014年北京卷文科的一道高考题:已知函数f(x)=2x3-3x.(1)求f(x)在区间[-2,1]上的最大值;(2)若过点P(1,t)存在3条直线与曲线y=f(x)相切,求t的取值范围;(3)问过点A(-1,2),B(2,10),C(0,2)分别存在几条直线与曲线y=f(x)相切?(只需写出结论)本题考查了函数的导数题型.对于导数问题,高考重点考查两方面的内容:(1)函数的单调性;     

曲线与其曲率圆

设一条曲线的方程为y=f(x).该曲线在点M(x_0,y_0)处的曲率圆在切点附近的一支曲线方程设为y=g(x),并设f(x)在x=x_0附近有三阶连续导数,且f″(x_0)≠0.将f(x)-g(x)在x=x_0处展开为二阶泰勒公式(注意到 f(x_0)=g(x_0),f′(x_0)=g′(x_0)及f″(x_o)=g″(x_0):     

非线性Chebyshev逼近的唯一性

§1.引言 设X是紧致Hausdooff空间,C(X)表示X上实值连续函数全体,带有一致范数 ||f||=max{|f(x)|:x∈X},f∈C(X).记 Z_f={x∈X:f(x)=0}, M_j={x∈X:|f(x)|=||f||}.又设l,u为X到拓广实数集[-∞,∞]的函数,l相似文献   

三次曲线切线的两个性质

文[1][2]给出了三次函数f(x)=ax~3 bx~2 cx d(a≠0)的对称中心为(-b/3a,f(-b/3a)),受此启发笔者对三次曲线的切线进行了研究,发现了如下两个性质,供读者参考.定理1已知三次函数f(x)=ax3 bx2 cx d(a≠0),A为曲线上的除对称中心外的任一点,在A点处的切线m交曲线于B,在B点的切线为n,kn,km表示两切线的斜率,则kkmn=4的充要条件是b2=3ac.图1定理1图证设A(x0,y0),∵f′(x)=3ax2 2bx c,∴km=3ax02 2bx0 c.切线m的方程:y-f(x0)=f′(x0)(x-x0),其中f′(x0)=3ax02 2bx0 c.联立方程y-f(x0)=f′(x0)(x-x0),y=ax3 bx2 cx d,解得:x=-2x0-ab,所以B点为(-…     

拟线性系统的概周期解的存在性

<正> 考虑拟线性微分方程系 dX/dt=A(t)X十f(t)十μF(X,t,μ),(1)其中A(t)是t的n阶连续方阵,x是n向量,f(t),F(X,t,μ)是各变量的n连续向量,μ真是小参数. 当A(t)是常数方阵,f(t),F(X,t,μ)是t的一致概周期向量函数,Coddington,Levinson,等人建立了(1)的周期解的存在定理.此可参考[1]和[2].对A(t)为常数方阵,f(t),F(X,t,μ)是t的一致概周期向量函数,更进一步建立了(1)的概周期解的存在定理.     

关于三次函数切线问题的思考

<正>2014年北京高考文数试卷的20题如下:已知函数f(x)=2x³-3x,(Ⅱ)若过点(1,t)存在3条直线与曲线y=f(x)相切,求t的取值范围.无独有偶,2016年沧州质检文科试卷上的21题与其相似:已知函数f(x)=ax3-3x,(Ⅱ)若过点(1,t)存在3条直线与曲线y=f(x)相切,求t的取值范围.无独有偶,2016年沧州质检文科试卷上的21题与其相似:已知函数f(x)=ax³-3x,g(x)=xlnx+63-3x,g(x)=xlnx+6^(1/2)/9,且函数y=f(x)与函数y=g(x)的图像在交点处存在公共切线,(Ⅱ)若     

有理曲线的多项式逼近

利用曲线摄动的思想给出了用多项式曲线逼近有理曲线的一种新方法．其基本步骤是对有理曲线的控制顶点进行摄动，使之产生一多项式曲线，并使摄动误差在某种范数意义之下达到最小．同时，通过适当控制摄动曲线的顶点，使逼近多项式曲线与有理曲线在两端点保持一定的连续性．这一结果可以与细分（ｓｕｂｄｉｖｉｓｉｏｎ）技术结合给出有理曲线的整体光滑的分片多项式逼近．实例表明，在某些情况下本文中的方法要优于传统的Ｈｅｒｍｉｔｅ插值方法及Ｔ．Ｗ．Ｓｅｄｅｒｂｅｒｇ和Ｍ．Ｋａｋｉｍｏｔｏ（１９９１）提出的杂交曲线逼近算法．     

General spectral flow formula for fixed maximal domain

We consider a continuous curve of linear elliptic formally self-adjoint differential operators of first order with smooth coefficients over a compact Riemannian manifold with boundary together with a continuous curve of global elliptic boundary value problems. We express the spectral flow of the resulting continuous family of (unbounded) self-adjoint Fredholm operators in terms of the Maslov index of two related curves of Lagrangian spaces. One curve is given by the varying domains, the other by the Cauchy data spaces. We provide rigorous definitions of the underlying concepts of spectral theory and symplectic analysis and give a full (and surprisingly short) proof of our General Spectral Flow Formula for the case of fixed maximal domain. As a side result, we establish local stability of weak inner unique continuation property (UCP) and explain its role for parameter dependent spectral theory. This work was supported in part by The Danish Science Research Council, SNF grant 21-02-0446. The second author is partially supported by FANEDD 200215, 973, Program of MOST, Fok Ying Tung Edu. Funds 91002, LPMC of MOE of China, and Nankai University.     

实分片代数曲线的拓扑结构

The piecewise algebraic curve is a kind generalization of the classical algebraic curve.By analyzing the topology of real algebraic curves on the triangles,a practi-caUy algrithm for analyzing the topology of piecewise algebraic curves is given.The algrithm produces a planar graph which is topologically equivalent to the piecewise algebraic curve.     

Gk保形分段2k次参数多项式插值

An interpolation scheme constructing shape preserving piecewise de-gree 2k parametric polynomial curves is presented. For the given data set {Qi＝(x1,yi) }n i-0, the shape preserving interpolation curve is Gk continuous.     

两类新的广义Ball曲线

本文提出两类新的广义Ｂａｌｌ曲线,一类介于Ｗａｎｇ（王国瑾）和Ｓａｉｄ广义Ｂａｌｌ曲线之间,另一类介于Ｂｅｚｉｅｒ和Ｓａｉｄ曲线之间,同时给出有关的升阶公式、递推算法及转化成Ｂｅｚｉｅｒ形式的系数公式。     

ISOGENOUS OF THE ELLIPTIC CURVES OVER THE RATIONALS

AbstractAn elliptic curve is a pair (E,O), where ?is a smooth projective curve of genus 1 and O is a point of E, called the point at infinity. Every elliptic curve can be given by a Weierstrass equationE:y2 a1xy a3y = x3 a2x2 a4x a6.Let Q be the set of rationals. E is said to be dinned over Q if the coefficients ai, i = 1,2,3,4,6 are rationals and O is defined over Q.Let E/Q be an elliptic curve and let E(Q)tors be the torsion group of points of E denned over Q. The theorem of Mazur asserts that E(Q)tors is one of the following 15 groupsE(Q)tors　Z/mZ, m = 1,2,..., 10,12,Z/2Z × Z/2mZ, m = 1,2,3,4.We say that an elliptic curve E'/Q is isogenous to the elliptic curve E if there is an isogeny, i.e. a morphism : E E' such that (O) = O, where O is the point at infinity.We give an explicit model of all elliptic curves for which E(Q)tors is in the form Z/mZ where m= 9,10,12 or Z/2Z × Z/2mZ where m = 4, according to Mazur's theorem. Morever, for every family of such elliptic curves, we give an explicit m     

Curvature driven flow of a family of interacting curves with applications

In this paper, we investigate a system of geometric evolution equations describing a curvature-driven motion of a family of planar curves with mutual interactions that can have local as well as nonlocal character, and the entire curve may influence evolution of other curves. We propose a direct Lagrangian approach for solving such a geometric flow of interacting curves. We prove local existence, uniqueness, and continuation of classical Hölder smooth solutions to the governing system of nonlinear parabolic equations. A numerical solution to the governing system has been constructed by means of the method of flowing finite volumes. We also discuss various applications of the motion of interacting curves arising in nonlocal geometric flows of curves as well as an interesting physical problem of motion of two interacting dislocation loops in the material science.     

Pre-compactness of isospectral sets for the neumann operator on planar domains

The Neumann operator maps the boundary value of a harmonic function tc its normal derivative. The inverse spectral properties of the Neumann operator associated to smooth, planar, Jordan curves are studied. The Riemann mapping theorem is used tc parametrize the set of planar Jordan curves by positive functions on the unit circle. By studying the zeta function associated to the spectrum, it is shown that isospectral sets of these functions are pre-compact in the topology of the L²-Sobolev space of order 5/2 - [euro]. Spectral criteria are given for the limiting curves of an isospectral set to be Jordan. A spectrally determined lower bound on the area of the interior of the curve is given.     

Cn-连续的B-型样条曲线及其局部性、插值与逼近

§ 1　IntroductionB-spline curve plays an important role in CAGD.Cn-continuous B-spline curve of de-gree n+ 1 has local support of length n+ 2 [1 ] .In order to modify the shape of a curve insmaller range,the length of its supportshould be as shortas possible.The interpolation ofa set of given data points with the B-spline curve generally needs to solve a system of lin-ear equations or to insert some additional control points[2— 5] .Besides,the global approxi-mation of the control polygon …     

New Trigonometric Basis Possessing Exponential Shape Parameters

Four new trigonometric Bernstein-like basis functions with two exponential shape parameters are constructed, based on which a class of trigonometric Bézier-like curves, analogous to the cubic Bézier curves, is proposed. The corner cutting algorithm for computing the trigonometric Bézier-like curves is given. Any arc of an ellipse or a parabola can be represented exactly by using the trigonometric Bézier-like curves. The corresponding trigonometric Bernstein-like operator is presented and the spectral analysis shows that the trigonometric Bézier-like curves are closer to the given control polygon than the cubic Bézier curves. Based on the new proposed trigonometric Bernstein-like basis, a new class of trigonometric B-spline-like basis functions with two local exponential shape parameters is constructed. The totally positive property of the trigonometric B-spline-like basis is proved. For different values of the shape parameters, the associated trigonometric B-spline-like curves can be $C^2$ ∩ $FC^3$ continuous for a non-uniform knot vector, and $C^3$ or $C^5$ continuous for a uniform knot vector. A new class of trigonometric Bézier-like basis functions over triangular domain is also constructed. A de Casteljau-type algorithm for computing the associated trigonometric Bézier-like patch is developed. The conditions for $G^1$ continuous joining two trigonometric Bézier-like patches over triangular domain are deduced.