CH₃COOH + Na \(\rightarrow\) CH₃COONa + \(\dfrac{1}{2}\)H₂

PT; C₂H₅0H + Na \(\rightarrow C_2H_5ONa\) + \(\dfrac{1}{2}\) H₂

ĐK để pt có 2 nghiệm x_1,x₂ là \(\Delta'\ge0\) \(\Leftrightarrow\) 6m+1\(\ge\) 0\(\Leftrightarrow m\ge\dfrac{-1}{6}\)

khi đó ; x₁ +x₂=\(\dfrac{2(m+1)}{m}\) [viet] \((1)\)

x₁.x₂=\(\dfrac{m-4}{m}\) \((2)\)

\(\Leftrightarrow m\)x₁.x₂=m-4

\(\Leftrightarrow\) mx₁x₂-m=-4

\(\Leftrightarrow m(\) x₁x₂ -1\()\) = -4

\(\Leftrightarrow m=\dfrac{-4}{x_1x_2-1}\) \((3)\)

thay [3] vào [1] ta đc; x₁+x₂=\(\dfrac{2.(\dfrac{-4}{x_1x_2-1}+1)}{\dfrac{-4}{x_1x_2-1}}\) [4]

\(\Leftrightarrow\dfrac{-4(x_1+x_2)}{x_1x_2-1}=\dfrac{-8+x_1x_2-1}{x_1x_2-1}\)

\(\Leftrightarrow-4(x_1+x_2)=x_1x_2-9\) là hệ thức cần tìm

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the question below.

Why is it that many teenagers have the energy to play computer games until late at night but can’t find the energy to get out of bed (35) ________ for school? According to a new report, today’s generation of children are in danger of getting so (36)_______ sleep that they are putting their mental and physical health at (37)_______. Adults can easily survive on seven to eight hours’ sleep a night, (38)_______teenagers require nine or ten hours. According to medical experts, one in five youngsters (39)________ anything between two and five hours’ sleep a night less than their parents did at their age. This (40) _____ serious questions about whether lack of sleep is affecting children’s ability to concentrate at school. The connection between sleep deprivation and lapses in memory, impaired reaction time and poor concentration is well (41) _______. Research has shown that losing as little as half an hour’s sleep a night can have profound effects (42) ______how children perform the next day. A good night’s sleep is also crucial for teenagers because it is while they are asleep (43)______ they release a hormone that is essential for their ‘growth spurt’ (the period during teenage years when the body grows at a rapid rate). It’s true that they can, to some (44) ______, catch up on sleep at weekends, but that won’t help them when they are dropping off to sleep in class on a Friday afternoon. By Tim Falla and Paul A.Davies, Solutions Advanced. OUP

Điền vào ô 36

A. few

B. little

C. less

D. Much

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from  45 to 54.

A survey is a study, generally in the form of an interview or a questionnaire, which provides information concerning how people think and act. In the United States, the best-known surveys are the Gallup poll and the Harris poll. As anyone who watches the news during campaigns presidential knows, these polls have become an important part of political life in the United States.

North Americans are familiar with the many “person on the street” interviews on local television news shows. While such interviews can be highly entertaining, they are not necessarily an accurate indication of public opinion. First, they reflect the opinions of only those people who appear at a certain location. Thus, such samples can be biased in favor of commuters, middle-class shoppers, or factory workers, depending on which area the news people select. Second, television interviews tend to attract outgoing people who are willing to appear on the air, while they frighten away others who may feel intimidated by a camera. A survey must be based on a precise, representative sampling if it is to genuinely reflect a broad range of the population.

In preparing to conduct a survey, sociologists must exercise great care in the wording of questions. An effective survey question must be simple and clear enough for people to understand it. It must also be specific enough so that there are no problems in interpreting the results. Even questions that are less structured must be carefully phrased in order to elicit the type of information desired. Surveys can be indispensable sources of information, but only if the sampling is done properly and the questions are worded accurately.

There are two main forms of surveys: the interview and the questionnaire. Each of these forms of survey research has its advantages. An interviewer can obtain a high response rate because people find it more difficult to turn down a personal request for an interview than to throw away a written questionnaire. In addition, an interviewer can go beyond written questions and probe for a subject’s underlying feelings and reasons. However, questionnaires have the advantage of being cheaper and  more consistent

The word "elicit" in line 15 is closest in  meaning to

A. rule  out

B. bring  out

C. predict

D. compose

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from  45 to 54.

A survey is a study, generally in the form of an interview or a questionnaire, which provides information concerning how people think and act. In the United States, the best-known surveys are the Gallup poll and the Harris poll. As anyone who watches the news during campaigns presidential knows, these polls have become an important part of political life in the United States.

North Americans are familiar with the many “person on the street” interviews on local television news shows. While such interviews can be highly entertaining, they are not necessarily an accurate indication of public opinion. First, they reflect the opinions of only those people who appear at a certain location. Thus, such samples can be biased in favor of commuters, middle-class shoppers, or factory workers, depending on which area the news people select. Second, television interviews tend to attract outgoing people who are willing to appear on the air, while they frighten away others who may feel intimidated by a camera. A survey must be based on a precise, representative sampling if it is to genuinely reflect a broad range of the population.

In preparing to conduct a survey, sociologists must exercise great care in the wording of questions. An effective survey question must be simple and clear enough for people to understand it. It must also be specific enough so that there are no problems in interpreting the results. Even questions that are less structured must be carefully phrased in order to elicit the type of information desired. Surveys can be indispensable sources of information, but only if the sampling is done properly and the questions are worded accurately.

There are two main forms of surveys: the interview and the questionnaire. Each of these forms of survey research has its advantages. An interviewer can obtain a high response rate because people find it more difficult to turn down a personal request for an interview than to throw away a written questionnaire. In addition, an interviewer can go beyond written questions and probe for a subject’s underlying feelings and reasons. However, questionnaires have the advantage of being cheaper and  more consistent

The word "exercise" in line 12 is closest in  meaning to

A. consider

B. design

C. utilize

D. defend

Mark the letter A, B, C or D on your answer sheet to show the underlined part that needs correction in each of the following questions.

A basic (A) knowledge of social studies, such as history (B) and geography, are (C) considered a basic part of the education of every child. (D)  

A. basic 

B. history

C. are 

D. child.

Mark the letter A, B, C or D on your answer sheet to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions.

Take your time, think the matter over carefully, and then tell me what you’ve decided.

A. Keep calm

B. Hurry

C. Come on

D. Don’t hesitate