\(A=\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^{100}}\)

\(\Rightarrow2A=1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{99}}\)

\(\Rightarrow2A-A=\left(1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{99}}\right)-\left(\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^{100}}\right)\)

\(\Rightarrow A=1-\frac{1}{2^{100}}\)

bn thay số vào mà tương tự nhé 

Quy đồng tử số:

25/37 (giữ nguyên)

5/6 = 25/30

Số a cần tìm là: 37 - 30 = 7

ĐS: 7

1. He was late so often that it was___that he would lose his job eventually.

a. forecast

b. anticipated

c. potential

d. inevitable

2. What do you say___going on a hike with me next Saturday?

a. at

b.to

c. by

d. on

3. I know David Fletcher___sight, but I've never been introduced to him.

a. at

b. in

c. by

d.on

4. There is a very ___rule forbidding smoking in bed.

a. strict

b. strong

c. hard

d. severe

5. She would like to live in a country___it never snows.

a. which

b. whose

c.who

d. where

6. The ink had faded with time and so parts of the letter were____.

a. illiterate

b. illegitimate

c. indelible

d. illegible

7. I may look half asleep, but I can assure you I'm ____awake.

a. broad

b. wide

c. full

d. well

8. She has no ____of saying such a thing.

a. reminder

b. recollection

c. souvenir

d. memory

9. It was raining so heavily that we could ___ahead of us.

a. hardly see nothing

b. hardly see something

c. hardly see anything

d. not hardly see everything

10. ____had the curtain been raised than the lights went out.

a. no sooner

b. hardly

c. only when

d. scarcely

11. My brother asked her to marry him but she turned him___.

a. over

b. aside

c. off

d. down

12. These are the only good books ___there are on the subject.

a. what

b. that

c. in which

d. of which

1. We learned at school that Shakespeare ___born in 1564.

a. was

b. got

c. would be

d. were

2. I am ___aware of the need to obey the rules of the competition.

a. much

b. far

c. greatly

d. well

3. He was seen___the room.

a. enter

b. enter into

c. to enter

d. to entering into

4. A motorbike is less___to run than a car.

a. experimental

b. expensive

c. explosive

d. external

5. A cold wind___for the last three days.

a. blows

b. has been blowing

c. is blowing

d.blew

6. I___that the score would be 2-0, but I was wrong.

a. told

b. prophesize

c. foretold

d. predicted

7. John studied hard at school,___at home he helped his mother with her work.

a. that

b. where

c. while

d. which

8. They had a quarrel but now they're the___of friends again.

a. best

b.most

c.surest

d. happiest

9. Nancy is now on very good____her friends.

a. term of

b. term to

c. terms with

d. terms of

10. We all laughed at his____of the teacher.

a. imitation

b. copy

c. mimic

d. image

11. As it was so hot in the office he____his tie.

a. left

b. loosened

c. slackened

d. unwired