Nếu tăng khoảng cách giữa hai điện tích điểm lên 4 lần thì độ lớn lực tương tác tĩnh điện giữa hai điện tích giảm là

A. 2 lần

B. 4 lần

C. 8 lần

D. 16 lần

a.x\(^6\)-y\(^6\)=(x\(^2\))\(^3\)+(y\(^2\))\(^3\) =(x\(^2\)+y\(^2\))(x\(^4\)-x\(^2\)y\(^2\)+y\(^4\))

b.x\(^{35}\)+x\(^{34}\)+......+x+1 =x\(^{34}\).(x+1)+......+(x+1)

=(x\(^{34}\)+x\(^{32}\)+......+x\(^2\)+1)(x+1)

c.x\(^2\)-6xy+9y\(^2\)-9 =x\(^2\)-2.3xy+(3y)\(^2\)-3\(^2\) =(x-3y)\(^2\)-3\(^2\)

=(x-3y-3)(x-3y+3)

d.(x-9)(x-7)+1 =x\(^2\)-7x-9x+63+1 =x\(^2\)-16x+64

=x\(^2\)-2.8x+8\(^2\) =(x-8)\(^2\)

B=(x-2)(x-4)+3=x^2-6x+9=(x-3)^2>=0

=>(x-2)(x-4)+3 luôn dương với mọi x

C=(x^2+2x+1)+(4y^2-4xy+x^2)+4

= (x+1)^2+(2y-x)^2+4

ta có : (x+1)^2+(2y-x)^2 >=0 với mọi x,y

=> (x+1)^2+(2y-x)^2+4 >=4 với mọi x,y

do đó C luôn dương với mọi x,y

Nhận định nào dưới đây là đúng về quyền bất khả xâm phạm về thân thể của công dân?

A. Trong mọi trường hợp không ai có thể bị bắt

B. Công an có thể bắt người nếu nghi là tội phạm

C. Trong mọi trường hợp, chỉ được bắt người khi có quyết định của Toà án

D. Chỉ được bắt người khi có lệnh của cơ quan nhà nước có thẩm quyền, trừ trường hợp phạm tội quả tang

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

          Franklin D. Roosevelt, the 32^nd President of the United States, was from a wealthy well-known family. As a child, he attended private school, had private tutors, and traveled with his parents to Europe. He attended Harvard University, and afterward studied law. At age 39, Roosevelt suddenly developed polio, a disease that left him without the full use of his legs for the rest of his life. Even though the worst of his illness, however, he continued his life in politics. In 1942 he appeared at the Democratic National Convention to nominate Al Smith for president, and eight years after that he himself was nominated for the same office. Roosevelt was elected to the presidency during the Great Depression of the 1930s, at a time when more than 5,000 banks had failed and thousands of people were out of work. Roosevelt took action. First he declared a bank holiday that closed all the banks so no more could fail; then he reopened the banks little by little with government support. Roosevelt believed in using the full power of government to help what he called the “forgotten people”. And it was these workers, the wage earners, who felt the strongest affection toward Roosevelt. There were others, however, who felt that Roosevelt’s policies were destroying the American system of government, and they opposed him in the same intense way that others admired him

          In 1940 the Democrats nominated Roosevelt for an unprecedented third term. No president in American history had ever served three terms, but Roosevelt felt an obligation not to quit while the United States’ entry into World War II was looming in the future. He accepted the nomination and went on to an easy victory

What does the passage mainly discuss?

A. political aspects of Roosevelt’s life

B. problems during the Great Depression

C. Roosevelt’s upbringing

D. criticisms of Roosevelt’s action

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.

Many people enjoy lying in bed in the morning, but can you imagine having to spend 90 days in bed? Could you stand the boredom and the frustration of not being(31)..... to get up? That was the task that faced 14 volunteers when they started out on a bed-rest experiment being conducted (32)….. the European Space Agency.

The study had a serious purpose: to investigate the changes that take place in the human body during long-duration spaceflight. Lying in a horizontal position was the best way of (33)…… weightlessness. The aim was to discover what effect period of weightlessness will have on the health of astronauts spending several months on the International Space Station.

The volunteers ate their meals, took showers and underwent medical tests without ever sitting up. That's even tougher than it sounds, especially when you (34) ..…. that no visitors were permitted. However, each volunteer did have a mobile phone, as well as access to the latest films, computer games and music. Surprisingly, Everyone was in a good (35) ..…. at the end of the 90 days, 'I would do it again,' said one of the volunteers. 'It was disorientating, but we knew we were 'contributing to medical research and space exploration.

Điền ô số 31

A. enabled

B. allowed

C. granted

D. approved