问题 单项选择题

则A与B()

A. 合同且相似

B. 合同但不相似

C. 不合同但相似

D,不合同且不相似

答案

参考答案:A

解析:

由于|λE-A|=λ4-4λ3=0

A的特征值为4,0,0,0.又因A是实对称矩阵,A必与对角矩阵

相似.所以A与B必相似.

因为A,B有相同的特征值,从而二次型xTAx与xTBx有相同的正、负惯性指数,从而A与B亦合同.故选A.

阅读理解

阅读理解。

     I had my first job at the age of thirteen, when a friend of my mother who owned a bookshop hired me

for six hours a week to help her in the shop. I was very proud to earn my own pocket money and my parents

never interfered (干涉) with how I spent it, even when I was spending it foolishly. They believed that by

earning money, spending it, and learning from the mistakes, I would become more mature and responsible

about how to handle work, relationships with others, and money.

     Like many American parents, my parents also let me and my brothers do things over which they worried

a great deal. When I was sixteen, for example, after I finished high school and before I entered university, I

wanted to spend the summer months traveling around Europe. My mother was against the idea of my traveling

alone at such a young age, but my father felt that it would be a great experience for me. In the end, my father

won the argument on the condition that I limited my traveling to France, my mother' s home, where I had

many uncles, aunts and cousins spread out through the country who could provide shelter and help if I needed

them.

     Three years later, my younger brother decided to take a year off after his first year in university and travel

through the United States and the Caribbean. Again my mother was very worried and not eager to see my

brother leave school, but my father encouraged him and my brother had a fascinating year working his way

on trains and ships to earn passage to different ports and cities, and discovering many fascinating places and

people.

     These kinds of experiences are probably rare for children in many countries but in the US they are fairly

common. Most parents start pushing their children at a young age to do small things by themselves. By the

time they have finished high school, many American kids have already had part-time jobs, traveled around the

US or other countries on their own, have selected the university they plan to attend and maybe even decided

on their future career, and so on.

1. The writer's parents allowed their kids to travel so that _____. [ ]

A. it could make the kids become braver

B. the kids could earn some pocket money

C. the kids could find jobs more easily

D. it could bring good to the kids' future

2. The writer thinks _____. [ ]

A. his brother gained valuable experiences during the travel

B. his brother earned a lot of money by working

C. his brother didn't disappoint his father

D. his brother's travel was better than his to France

3. Which of the following statements is True? [ ]

A. The author went to France in order to see his relatives.

B. The author's mother managed to stop the kids doing dangerous traveling.

C. The author's brother gave up his university to travel in the USA and the Caribbean.

D. Many American parents encourage their kids do things independently to prepare for the future.

4. The text is mainly about the writer and his brother's stories to _____. [ ]

A. do some part-time jobs

B. become independent

C. travel for experiences

D. earn pocket money

单项选择题