Gọi x là chiều rộng hình chữ nhật ( x > 0 )

Chu vi hình chữ nhật là:
( 15 + x ) x 2 = 48
30 + 2x = 48
2x = 48 - 30
2x = 18
x = 18 : 2
x = 9 (cm)
Vậy chiều rộng hình chữ nhật là 9 cm

Diện tích hình chữ nhật là:
15 x 9 = 135 (cm²)
Vậy diện tích hình chữ nhật là 135 cm²

Xin lỗi nếu tôi giải hơi kiểu loằng ngoằng với không đúng cách một chút=))

A It was so bad weather -> The weather was so bad

\(a.\) \(\left(-\dfrac{3}{4}\right)+\dfrac{2}{7}+\left(-\dfrac{1}{4}\right)+\dfrac{3}{5}+\dfrac{5}{7}\)

= \(\left[\left(-\dfrac{3}{4}\right)+\left(-\dfrac{1}{4}\right)\right]+\left(\dfrac{2}{7}+\dfrac{5}{7}\right)+\dfrac{3}{5}\)

= \(\left(-1\right)+1+\dfrac{3}{5}\)

= \(\dfrac{3}{5}\)

      \(\dfrac{11}{15}-x=\dfrac{2}{3}\)

<=> \(x=\dfrac{11}{15}-\dfrac{2}{3}\)

<=> \(x=\dfrac{11}{15}-\dfrac{10}{15}\)

<=> \(x=\dfrac{1}{15}\)

Vậy chắc đúng chính tả thì bạn thượng đẳng hơn những người khác hả bạn?

1. Let’s …………… some oranges.

A. bought

B. buying

C. to buy

D. buy

2. Jacques Cousteau ………………. a deep sea diving vessel in the early 1940s.

A. explored

B. invented

C. discovered

D. found

3. My father is a ……………………tennis player.

A. skillful

B. carefully

C. skill

D. skillfully

4. There are many good programs ........................teenagers.

A. on

B. for

C. to

D. about

5. Forty years ago, very few people………………….TV sets.

A. had

B. have

C. has

D. having

6. Hoa enjoys……...........books very much.

A. to read

B. read

C. reads

D. reading

7. My brother doesn’t like pork and ……………

A. either do I

B. neither do I

C. neither I do

D. I don’t too

8. Liz didn’t ……………..fish for her lunch.

A. ate

B. do

C. eat

D. eating

9. The nurse told Hoa……..…..to the waiting room.

A. to return

B. returning

C. return

D. returned

10. They …………… video games now.

A. play

B. plays

C. will play

D. are playing

11. (moderate) ...............................in eating is very important.

A. Moderate

B. Moderating

C. Moderation

D. Moderately

12. You must wash the spinach........................

A. careless

B. carelessly

C. careful

D. carefully

13. Sugar is not a(n) ...............................................(health) good.

A. health

B. healthy

C. unhealthy

D. healthily

14. There was a good select ....................... of meat on the stall.

A. select

B. selection

C. selecting

D. to select

15. There was a district walking ........................ for school children last year.

A. compete

B. competitor

C. competition

D. competitions

16. She watched TV last night. Her mother watched TV last night.

A. She watched TV last night. Her mother is, too.

B. She watched TV last night. Her mother does, too.

C. She watched TV last night. So does her mother.

D. She watched TV last night. So did her mother.

17. My sister can’t swim. I can’t swim.

A. My sister can’t swim. I can’t, too.

B. My sister can’t swim. I can, too

C. My sister can’t swim. Neither can I

D. My sister can’t swim. Neither can’t I

18. Hoa learns English well.

A. Hoa is a good English learner.

B. Hoa is a well English leaner.

C. Hoa is good learner English

D. Hoa is well learner English.

19. How heavy are you?

A. What is your weigh?

B. What is your weight?

C. What are your weight?

D. What is your heavy?

20. Don’t forget to turn off the light before going out.

A. Don’t turn off the light before going out.

B. You shouldn’t turn off the light before going out.

C. Remember to turn off the light before going out.

D. Remember turn off the light before going out

2. to

3. at

4. at

5. at

6. at

7. to

8. to

9. to

10. for

Có : △ = ( -2m )² - 4.1.( -4m - 4 )
            = 4m² + 16m + 16
            = ( 2m )² + 2.2m.4 + 4²
            = ( 2m + 4 )² > 0
-> △ > 0 => Phương trình luôn có 2 nghiệm phân biệt