Bài 11 : Tìm GTNN của của các biểu thức sau :

a ) \(A=\left|x+3\right|+\left|2x-5\right|+\left|x-7\right|.\)

b ) \(B=\left|x+2\right|+\left|3x-4\right|+\left|x-2\right|+5\)

c ) \(M=\left|x+2\right|+\left|x-3\right|\)

d ) \(C=\left|2x+5\right|+\left|2x+1\right|+\left|2x-7\right|+\left|2x-4\right|+4\)

e ) \(D=\left|3x-6\right|+\left|3x-9\right|+\left|3x-12\right|+\left|3x-15\right|+2018\)

Bài 4 : Tìm \(x\), biết :

a ) \(\left|4-2x\right|+\left|x+3\right|=8\)

b ) \(\left|x+1\right|+\left|x-2\right|+\left|x+3\right|=6\)

c ) \(\left|x-2\right|+\left|x-3\right|+\left|4-x\right|=2\)

d ) \(2\left|x+2\right|+\left|4-3x\right|=11\)

e ) \(\left|2x-1\right|+\left|2x-5\right|=4\)

g ) \(\left|x-3\right|+\left|3x+4\right|=\left|2x+1\right|\)

Bài 2 : Rút gọn biểu thức sau :

a ) \(A=\left|x+1,3\right|-\left|x-2,5\right|.\)khi \(x< -1,3\)

b ) \(D=\left|x+3\frac{1}{2}\right|+\left|x\right|-3\frac{1}{2}\)với \(x>0\)

c ) \(A=\left|x-\frac{1}{7}\right|-\left|x+\frac{3}{5}\right|+\frac{4}{5}\)khi \(-\frac{3}{5}< x< \frac{1}{7}\)

Ex1:Use the correct tense of the verb in bracket.

1. You ever (do) ……………….volunteer work? – Yes, I (do) ……volunteer work last month.

2. I (collect)…………..hundreds of old books and clothes for street children so far.

3. My sister wants  to raise .funds for elderly and disabled people so she (make) ………..hundreds of postcards to sell them.

4. My hobby is carving eggshells and now I (carve) …………nearly 100.

5. Going home from school yesterday, I (help) …………….an old man to go across the street.

6. Last Tuesday, I (go) ………….home late because there (be) ………a traffic jam near my school.

7. At Tet, my mother and her close friends often  goes  to the hospitals to donate cakes, sweets and toys for the sick children there. She (do) ……………..…..it for many years.

8. Lan never (eat) …… Banh tet. She will try it this year.

9. Linh is my close friend.We(know) …each other since 2012.

10. They (not see)……………..the film Titanic yet.

11. Tom( not call)………………his boss recently.

12. John( read)………………..the letter from Mary already.

13. We(not begin)…………….to learn for the test yet.

14.I( meet)………..Robert at the supermarket this morning.

15. Nancy(be)…………………to VietNam several times.

16. I(not see)…………your brother yet.

17. My pen isn’t here any more. Someone(take)….it already.

18. When…………your father(give up)………….smoking?

19. The motorbike looks clean. .(you/ wash)…………..it?

20. My uncle(move)……………to Da Lat in 2005.

21. The Greens(be)……to many countries in the world so far.

22. We(go)..to that village to do volunteer work several times.

23. We(spend)….…our summer vacation in HL Bay last July.

24. Our teacher (explain)..to us how to use the printer already.

25. The postman(deliver)…………the letter half an hour ago.

26. Mai(not finish)…………………her homework yet.

27. I(visit)………our form teacher in the hospital already.

28. I(hear)……the good news fro Mary a few minutes ago.

29. They (not start)…………..the project yet.

30. We (just take)………………….up the community service.