a, 7x^3 + 5 ( x - y )^2 v- 7y^3
= 7 ( x^3 - y^3 ) + 5 ( x-y )^2
= 7 ( x - y )^3 + 5 ( x-y ) ^2
= [ 7 ( x- y ) + 5 ] ( x-y) ^2

1. Ta có : A = x^4 - 8x^2 +2
= ( x^2 )^2 - 2.x^2.4 + 8 - 6
= ( x^2 - 4 ) ^2 -6
Vì ( x^2 - 4 ) ^2 > hoặc = 0 vs mọi x ( " lớn hơn hoặc bằng " bn ghi kí hiệu nhé
=> ( x^2 - 4 )^2 -6 > hoặc = -6 vs mọi x
=> A > hoặc = - 6 vs mọi x
Vậy GTNN của A = -6 => ( x^2 - 4 )^2 = 0 .... ( bn tự giải nhé )

21. since I have been to a Chinese restaurant
22. came here since 1986
23. haven't met for a long time since our last conversation
24. us to go by train
25. After Julia had cleaned the house, she went shopping
26. Jim was travelling in Paris, she bought a new car
27. a new car after she had checked all the prices
28. has been to Vietnam for 3 years
29. had left the office before they finished work
30. learnt E for 5 years

cau 4 chua nghi ra

3. Aretha has never taken any classes so she can't pass the test

Bài 1 :
F - T - F - F - F - T - F - T - F
Bài 2 :
1. .... play badminton well
2. ... need to drive so fast
3. ... me to show my homework
4. ... is neccesary to keep the environment clean
5. ... will be shown to the public when they finish it
6. ... you rest ur self, you will be ill
7. ... you didn't make any noise,...
8. chịu :)

nguyen thi thu thuy copy ac nhi?con doi tick nua chu!!!du sao cung thong minh nen tuj tick cho :V

1. stay ( must + V )
2. go ( sau Let's + V )
3. sing
4. dancing ( câu gợi ý )
5. playing
6. go
7. isn't
8. is / is
9. Do / go camping ( always => h/tại đơn )
10. Does / plant
11. - does / do ( often => h/tại đơn )
- watches / reads
12. is / isn't working ( at the moment => h/tại típ diễn )
13. don't go
14. plays / flies