70000 nha em lúc nào chơi gái thì gọi chị nha chị giảm giá cho nhé thanks

700 nha bạn 

Câu 1 : 

a, \(A=\left(\frac{1}{\sqrt{a}-1}+\frac{1}{\sqrt{a}+1}\right).\frac{1}{\sqrt{a}}\)

\(=\left(\frac{\sqrt{a}+1}{a-1}+\frac{\sqrt{a}-1}{a-1}\right).\frac{1}{\sqrt{a}}=\frac{2\sqrt{a}}{a-1}.\frac{1}{\sqrt{a}}=\frac{2}{a-1}\)

b, Ta có :A = 1 hay  \(\frac{2}{a-1}=1\Leftrightarrow a-1=2\Leftrightarrow a=3\)( tmđkxđ )

Câu 3 : 

\(\hept{\begin{cases}2x-3y=1\left(1\right)\\3x+y=7\left(2\right)\end{cases}}\)Ta có : \(y=7-3x\)(k)

Thay vào phương trình 1 ta được : 

\(2x-3\left(7-3x\right)=1\)

\(\Leftrightarrow2x-21+9x=1\Leftrightarrow11x=22\Leftrightarrow x=2\)

Thay vào (k) ta được : \(y=7-3.2=7-6=1\)

Vậy \(\left\{x;y\right\}=\left\{2;1\right\}\)

KẾT QUẢ LÀ 439089

439089 là kết của phép tính trên

Kẻ \(AH\perp DC\) , \(BK\perp DC\)

Xét tứ giác ABKH có: AB // HK (gt)

                                   AH // BK ( cùng \(\perp DC\))

=> ABKH là hình chữ nhật (dhnb)

=> HK = AB = 4, AH = BK

Xét △ ADH vuông tại H và △BCK vuông tại K

Có: AH = BK (cmt)

      AD = BC (ABCD là hình thang cân)

=> △ADH = △BCK (ch-cgv)

=> DH = KC

Ta có: DH + HK + KC = DC

=> 2DH + HK = 10

=> 2DH + 4 = 10

=> 2DH = 6

=> DH = 3 = CK

Ta có: DK = DH + HK = 3 + 4 = 7

Xét △DEF vuông tại F có: BF là đường trung tuyến

=> BF = BD = DE/2

=> △BFD cân tại B

mà BK là đường cao ( \(BK\perp DF\))

=> BK là đường trung tuyến

=> DK = KF = 7

Ta có: CF = KF - KC = 7 - 3 = 4

MI = MP/2 = (MN+NP)/2 = (3+5)/2 = 4 

có biết cái gì đâu mà làm!

yeu con cho 

b) Chắc đề bài bạn gõ sai, phải là \(AM.BN=\frac{AB^2}{4}\).

Gọi giao giữa tiếp tuyến \(MN\)và \(\left(O\right)\)là \(H\).

Tam giác \(MON\)vuông tại \(O\), đường cao \(OH\)nên có: 

\(MH.NH=OH^2\)

mà \(MA=MH,NB=NH\)(tính chất 2 tiếp tuyến giao nhau) , \(AB=2R\)suy ra

\(AM.BN=MH.NH=OH^2=R^2=\frac{AB^2}{4}\)

Exercise 3:  Choose the best one (A, B, C or D) to complete the sentence.

1. They repaired the furniture in our village school and also _______the houses for elderly people.

A. fixed             B. removed        C. renewed                    D. regenerated

2. Care _________ the young and the old is a public responsibility.

A. with              B. for                C. to                             D. about

3. They had found ways to ________funds to support their activities.

A. rise               B. collect          C. gather                       D. raise

4. They ________  a  lot of  flowers in their garden and around their house.

A. place            B. plant             C. put                           D. pick down

5. She has only to ________ the meals, look after the children, and keep the house in order.

A. take              B. cook             C. do                            D. make

6. Girls may also be made to do chores when they could be learning, and not be allowed to take ______ sports.

A. part in           B. one in           C. into                           D. take for

7.  They want prosperity but  they also want a ______ environment, good health, social protection.

A. cleaning        B. cleaned         C. clean                        D. cleanness

8. He ______  thousands of pounds to charity.

A. put               B. donated        C. transmitted                D. took

9. At Tet, my mother and her close friends often go to the hospitals to donate cakes, sweets and toys for the sick children there. She  _________ it for many years.

A. is doing         B. have done     C. has done                   D. did

10. The volunteers have raised funds to _________ homeless people.

A. bring             B. help              C. rescue                      D. bear

11. The last aim is to _______ fresh drinking water at the lowest cost possible.

A. do                B. make            C. provide                      D. give

12. Mr. Brown and some ________ are on a very dirty beach now to ________ the beach a clean and beautiful place again.

A. volunteers - make                  B. volunteering - get       C. voluntary - do                         D. volunteer - change

13. It is very positive for children to study hard if they’re ________ to do so.

A. exciting         B. interesting     C. eager                        D. bored

14. Vietnamese people have had the __________of helping one another since the early days of the country.

A. custom         B. legend          C. tradition                    D. religion

15. A volunteer always helps other people willingly and ____ payment.

A. for               B. within             C. about                        D. without

16. They save  people money as well as having health ________.

A. benefits         B. forces           C. problems                   D. events

17. They volunteer by ______ children from poor families in their community.

A. talking          B. singing          C. encouraging              D. tutoring

18. All the members have to collect glass, waste paper and empty cans and send them for _____.

A. recycling       B. reusing         C. producing                  D. reselling