习题与补充题 习题 1.证明a(t)是常向量的充要条件是a(t)=0 2.设是常数,a是常向量,证明 (1) d (or(t)= (2)((t)a)=t)a0 3.下列等式成立吗?为什么? (1)r2= (3)F= dt 4.设向量函数a(t)满足aa=0,axa,证明a(t)是常向量。 5.证明r()=(2t-1,t2-2,-t2+4t)为共面向量函数。 6.证明:F(t)=at3+bt2+ct,为共面向量函数的充要条件是abc)=0 7.试证明

一、选择题 A型题 1.a2.c3.b4.c5.a6.b7.e8.b9.c10.d11.a 12.d13.d14.d15.c16.c17.a18.d19.b20.b21.d 22.D23.D24.E25.D26.C27.b28.d29.c30.a31.c

A-1磁场和磁路 A-2铁磁物质的磁化曲线 A-3磁路的基本定律 A-4恒定磁通磁路的计算 A-5交变磁通磁路简介 A-6铁/线圈

Problem Set 4 Solutions Due: Monday, February 28 at 9 PM Problem 1. Prove all of the following statements except for the two that are false; for those, provide counterexamples. Assumen 1. When proving each statement, you may assume all its predecessors (a)a =(mod n) Solution. Every number divides zero, so n (a-a), which means a a (mod n). (b)a≡b(modn) impliesa(modn)

第八章有理整数环 8-1有理整数环的基本概念 8.1.1有理整数环的基本概念 全体整数所组成的集合中有两种运算:加法和乘法,而且它们满足下面运算法则: （1)加法满足结合律; （2)加法满足加换律 （3)有一个数0,是对任意整数a,0+a=a; （4)对任意整数a,存在整数b,使b+a=0 （5)乘法满足结合律 （6)有一个数1,是对任意整数a,la=a

1 The Number-Picking Game Here is a game that you and I could play that reveals a strange property of expectation. 3, First, you think of a probability density function on the natural numbers. Your distri- bution can be absolutely anything you like. For example, you might choose a uniform distribution on 1, 2, ... 6, like the outcome of a fair die roll. Or you might choose a bi- probability, provided that,...,n. You can even give every natural number a non-zero nomial distribution on 0, 1 he sum of all probabilities is 1

The expectation or expected value of a random variable is a single number that tells you a lot about the behavior of the variable. Roughly, the expectation is the average value, where each value is weighted according to the probability that it comes up. Formally, the expected value of a random variable r defined on a sample space s is: (B)=∑R()Pr(o) To appreciate its signficance, suppose S is the set of students in a class, and we select a student uniformly at random. Let r be the selected student's exam score. Then

A prolapse is a downward or forward displacement of one of the pelvic organs from its normal location. *A variety of terms are used to describe female genital prolapse. *A cystocele is a downward displacement of the bladder. *A cystourethrocele is a cystocele that imcludes the urethra as part of the prolapsing organ complex

assets An asset is a commodity that provides a flow of services over time. +E.g. a house, or a computer. .A financial asset provides a flow of money over time -a security

Cloning vectors: 克隆载体 to clone a gene in a vector Expression vectors: 表达载体 to express a gene from a vector Integration vectors: 整合载体 to integrate a gene in a genome through a vector Cloning vectors 1 Plasmid vecters 2 Bacteriophage vectors 3 Cosmids & BACs 4 Eukaryotic vectors Cloning vectors: allowing the exogenous DNA to be inserted, stored, and manipulated mainly at DNA level. expression vectors: allowing the exogenous DNA to be inserted, stored, and expressed