`ABCD` là hình thang

`=>` AB // CD

`=>` Góc  `ABD` `=` góc `BDC` ( so le trong )

Ta có :

AB/BD `=9/12` `=3/4`

BD/DC `=12/16` `=3/4`

`=>` AB/BD `=` BD/DC

Tam giác ABD và tam giác BDC có :

BD/DC `=` AB/BD

`=>` Góc `ABD` `=` góc `BDC`

`=>` Tam giác `ABD` đồng dạng tam giác `BDC`

Tham khảo hình!

`@Nae`

`1).`

Ta có: `AB=AD+DB=9,5+28=37,5`

`\triangle ABC` có: `DE////BC`, theo hệ quả của định lí Ta-lét:

`(AD)/(AB)=(DE)/(BC)`

`=>(9,5)/(37,5)=8/x`

`=>x=(37,5.8)/(9,5)`

`=>x=600/19`

`2).`

`\triangle OKN` có: `LM////ON` theo hệ quả của định lí Ta-lét:

`(KO)/(KM)=(KN)/(KL)=(ON)/(LM)`

`=>25/10=y/16=45/x`

`=>y/16=45/x=5/2`

Với `y/16=5/2=>y=(16.5)/2=40`

Với `45/x=5/2=>x=(45.2)/5=18`

`3).`

Ta có: `ST \bot PQ` và `RP \bot PQ`

`=>ST //// RP`

Có: `QR=QS+SR=5+3,5=8,5`

`(QT)/(QP)=(QS)/(QR)`

`=>4/y=5/(8,5)`

`=>y=(4.8,5)/5`

`=>y=6,8`

`@Nae`

Áp dụng công thức tính chiều cao của hình thang là :

`H=S:a` nên ta có :

Chiều cao của hình bình hành đó là :

`140:10=14(dm)`

`@Nae`

Viết chữ thế này thì khó nhìn ra quá bạn Thịnh ơi :) nhắc cho phải sửa đi nhe :) 

Đường cao của tam giác đó là :

`50xx2:8=12,5(cm)`

Diện tích tam giác ABC đó là :

`(24xx12,5):2=150(cm`²`)`

Đáp số : ....
`@Nae`

`1.A`  `2.D`

`3.C`  `4.B`

`@Nae`

4. If I ____ him yesterday, I would have to come back tomorrow
A. didn’t meet B. have met C. met D. hadn’t met
5. If she ____ the truth, I think she’d never want to see you again
A. would know B. knows C. will know D. knew
6. I would never have believed ____ it with my own eyes
A. if I didn’t see B. if I hadn’t seen
C. if I haven’t seen D. if I wouldn’t have seen
7. Kevin never seems to get tired. I wish I _____ his energy
A. can have B. have had C. had D. would have
8. If _____ as I told her, she would have succeeded.
A. she has done B. she had done
C. she does D. she did
9. She would give them all that money now if we _____ her before.
A. wouldn’t advise B. won't advise
C. hadn't advised D. didn't advise
10. If I ________ an Angel, I __________to make all the children happy.
A. am/ will try B. have been/ would try
C. were/would try D. had been/would have tried
11. John would be taking a great risk if he _____ his money in that business.
A. would invest B. invested C. had invested D. invests
12. The car ________ if somebody takes it there.
A. will be repaired B. would be repaired
C. will been repaired D. is repair
13. You ______ to prison if you did that.
A. would be sent B. would have been sent
C. would be sent D. were sent

`@Nae`

`4/7xx` `x-2/3=1/5`

`7/7xx` `x=3/15+10/15`

`4/7xx` `x=13/15`

`x=13/15:4/7`

`x=13/15xx4/7`

`x=91/60`

Vậy `x=91/60`

`@Nae`

Độ dài đường chéo thứ nhất :

`(3/4+2/7):2=29/56(m)`

Độ dài đường chéo thứ hai :

`3/4-29/56=13/56(m)`

Diện tích vườn hoa hình thoi đó là :

`13/56xx29/56:2=377/6272(m^2)`

`@Nae`