Chào bạn

Ta có \(x^3+y^3=\left(x+y\right)^3-3xy\left(x+y\right)\)

* Thế \(x+y=1\) và \(xy=\left(-1\right)\) vào vế trái ta có

\(1^3-3.\left(-1\right)\left(1\right)=1-\left(-3\right)=1+3=4\)

Vậy 4 là giá trị của biểu thức \(x^3+y^3\) tại \(x+y=1\) và \(xy=\left(-1\right)\)

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V. In each of the following sentences, put the verb in brackets into the correct form.

1. have 4. have 7. is 10. are

2. is 5. are 8. have

3. do 6. has 9. has

V)

1. goes 8. has 15. has

2. wear 9. aren’t 16. is (was)

3. makes 10. was 17. is (was)

4. are 11. are 18. has

5. cause 12. is 19. are (were)

6. is 13. is 20. has

7. are 14. is

IV. Complete the sentences with is/ are, has/have or does do

1. have 4. have 7. is 10. are

2. is 5. are 8. have

3. do 6. has 9. has

III. Correct the sentences with is/ are, has/have or does/do

1. has-have 8. is-are 15. are-is

2. language-languages 9. √ 16. √

3. is-are 10. √ 17. admire-admires

4. √ 11. have-has 18. √

5. are-is 12. √ 19. were-was

6. is-are 13. was-were 20. are-is

7. have-has 14. is-are

II. Supply the correct tenses and form of the verbs in the parentheses:

1. are 8. was chosen; was chosen; were 15. is

2. is spent; is 9. encourages 16. has

3. hasn’t finished; has 10. saw; was trying 17. has

4. is closed 11. have 18. has

5. have tried 12. is 19. is

6. was stolen 13. has 20. has

7. does physics 14. have cause