已知三元二次型xTAx的平方项系数均为0,并且α=(1,2,-1)T满足Aα=2α.

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问题:

已知三元二次型xTAx的平方项系数均为0,并且α=(1,2,-1)T满足Aα=2α.
(Ⅰ) 求该二次型表达式;
(Ⅱ) 求正交变换x=Qy化二次型为标准形,并写出所用坐标变换;
(Ⅲ) 若A+kE正定,求k的值.

考点:普通考研考研数学(二)考研数学二
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给下列的图片选择对应的介词。
( ) 1. A. on
( ) 2. B. in
( ) 3. C. under                                                      
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()强调研究者与被研究者在时空上完全隔离开来,不存在互动的一种研究方法

A.调查法

B.现场法

C.隐蔽法

D.人种学研究

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“I find myself glancing at my watch to see how long I’ve been standing in line,” she said. “Everywhere I go, I notice if the dumpster(垃圾罐)gates are open or if there’s trash in the parking lot.” Ms. Clark is a “mystery shopper”, one of thousands of contract workers that companies hire to pretend as regular customers in order to judge customer service, cleanliness and whether a store is selling a product that meets company specifications (规格).

Mystery shoppers can be found or, rather, not found, everywhere from restaurants and automotive shops to convenience stores and department stores. They play a constant cat-and-mouse game with store and restaurant employees and managers. However it’s not all fun and games. Once in the field, a mystery shopper will typically visit several stores or restaurants per hour, taking mental notes while inside, then jotting down physical notes after they leave.

It’s important for mystery shoppers to be as exact as possible, because the client companies are looking for data they can use to improve their service. The questionnaire won’t say, “Does the trash can need to be emptied?” What an educated shopper will say is, “The trash can to the left of the front door was overflowing with 10 pieces of trash on the ground.” Companies don’t need opinion but facts.

Nowadays mystery shoppers are armed with a number of high-tech devices, such as a digital scale and a digital thermometer, as well as a handheld PC for recording the entire experience. It’s a challenging job but a rewarding one. Mystery shoppers can be full time or part time, but the full-time workers tend to stick to standard mystery shopping while part-timers often choose the less complex reward-based programs. In those , the shoppers stay disguised(装扮的) only until the “shop” is finished, and then reveal (透漏) themselves to the store management and award prizes to employees who provided excellent service.

To be a mystery shopper, it’s important to be a good observer, but sometimes it’s important to have the right profile(外表), too. Companies often hire shoppers from particular backgrounds to better blend in with clients’ regular customers. If a secret shopper will be sent in, for example, to do a high-end automotive shop, the candidate must have a particular profile that meets a high-end, luxury car-type buyer profile. “It’s a challenge to perform your shop without being discovered,” Ms. Clark said, “because most of the people that we work for are very aware of the mystery shopping program.”

67. According to the text a “mystery shopper” would not have to        .

A. sign a contract with the employer     B. travel a lot around the city

C. provide exact facts to the company D. fill in questionnaires  

68. We learn from the text that Ms. Clark        .

A. visits some shops regularly and sometimes does something special

B. pretends to be a shopper and evaluates the services

C. is a government official looking into the services

D. is a manager of a company offering good services

69. People are willing to become a mystery shopper mainly because they can        .

A. get the best service and get paid at the same time

B. play a cat-and-mouse game with shop employees and managers

C. do the job either full time or part time and get paid well

D. observe clearly what happens in the shops

70. What does the underlined word “those” in the 4th paragraph refer to?

A. The shops where the mystery shoppers go.      

B. The less complex reward-based programs.

C. Part-time jobs.             

D. Excellent services.

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咏梅绝唱“疏影横斜水清浅,暗香浮动月黄昏”出自()诗()。

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EDI是指

A) 即时库存管
B) 电子数据交换
C) 电子订货系统
D) 电子转账系统

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