user-avatar
Trungtien2020
2 năm trước
KHÔNG CẦN GIẢI RA, CHỈ CẦN NHẬN XÉT LỜI GIẢI ĐÚNG HAY SAI MỘT CÁCH TỈ MỈ LÀ ĐƯỢC!!! TỈ MỈ, RÕ RÀNG NHA, CẢM ƠN!!! đề bài: cho tam giác ABC. điểm D chia trong AB theo tỉ số 1:2, Echia trong AC theo tỉ số 2:5 DEgiao BC tại F. Tính BF:FC? GIẢI: Qua B kẻ BK //EC giao EF=K(K thuộc EF); qua B kẻ BM//EF giao AC=M(M thuộc AC). vì tam giác ECF có BM//EF=> FB/FC=EM/EC (theo định lý Ta lét) vì tam giác EFC có BK//EF( giả thiết) =>> FK/EF=FB/FC=KB/EC(hệ quả định lý Ta lét) Vì điểm D chia trong AB theo tỉ số 1:2=>AD/DB=1/2=>AD/AB=AD/(DB+AD)=1/(1+2)=1/3 vì điểm E chia trong AC theo tỉ số 2:5=>AE/EC=2/5=>AE/AC=AE/(EC+AE)=2/(5+2)=2/7 vì tam giác ABM có DE//BM(BM//EF mà D lại thuộc EF) => AD/BD=AE/EM=>>AE/EM=1/2=>FM=2AE (1) vì AE/EC=2/5(giả thiết)=>EC=5AE/2 (2) từ (1) và(2)=> EM/EC=2AE/5AE/2=4/5 vì FB/FC=EM/EC(chứng minh trên)=> FB/FC=4/5
Thích Trả lời Chia sẻ

Các câu hỏi liên quan

I / Choose the best option A,B,C, or D to complete each of the following sentences(Chọn câu đúng): 1/I’m going away……..........a few days. a.since b.in c.for d.during 2/My friend suggested ......................….by car. a.togo b.go c.going d.goes 3/Cool and burns immediately so as to… tissue damage. a.ease b.relieve c.minimize d.maximize 4/The lane is…... …Nguyen Trai street and Tran Hung Dao street. a.near b.between c.beside d.on 5/.I ..... on a farm when I was a young girl. a.use to living b.use to live c.used to live d.used to living 6/Would you mind………... .the windows. a.to close b.closing c.close d.closed 7/There are flights daily to Ho Chi Minh city…… Monday. a.besides b.after c.except d.on 8/My friend suggested............... ..by car. a.togo b.go c.going d.goes 9/Na………me wave to her. She………… …....in the other direction. a.see/is looking b.didn’t see/was looking c.was seeing/looked d.doesn’t see/looks 10/It’s ….to travel around Vietnam. a.interesting b.interested c.interestingly d.interestedly 11/……… ....you mind if I smoke? a.could b.don’t c.do d.would 12/Milk…… …to the houses by the milkman everyday. a.bring b.is bring c.is brought d.has brought 13/Milk bottles can be…… after being cleaned. a.recycled b.thrown away c.broken d.reused 14/I take part……. most youth activitives of my school. a.of b.on c.to d.in 15/This project…… .next month. a.is carried out b.will carried out c.carries out d.will be carried out 16/There are flights daily to Ho Chi Minh city.......... Monday. a.besides b.after c.except d.on 17/We were looking forward to….you in June. a.seeing b. see c.saw d.be seen 2.His parents are always proud..... ....him . a.about b.of c. on d.with 18/I will come and……… ..at 7 o’clock. a.pick up you b.pick you up c.see up you d.see you up 19/Today I went on …… .tour around Asia. a. a eight hours b.a eight hour c.an eight hours d.an eight hour 20/The teacher…… .a class at eight o’clock yesterday evening. a.is having b.was having c.has d.has had 21/…… ..I was having dinner,my husband was watching TV. a.While b.If c.Because d.As 22/Yesterday Lan went to the market and… some food. a.buy b.have bought c.buyed d.bought 23/Cool and burns immediately so as to....... tissue damage. a.ease b.relieve c.maximize d.minimize 24/How do you ……… ….about the people living here? a.fell b.fall c.feel d.felt 25/How many………………………………......................……… in the last competition? a.activities were there b.activities there were c.activities are there d.activities there are 26/How were the activitives……… .? a.organized b.made c.put d.done 27/The cupboard is open and everything.. a.is broken b.was broken c.has been broken d.would be broken 28/Is Ha Long Bay a… ..Heritage? a.World Natural b.Natural World c.World Cutural d.Cutural World 29/She has...... ...over 30 pages since yesterday. a.writen b.wrote c.written d. write

2.1. Mức độ nhận biết 1. Let’s to go abroad for our summer vacation this year A B C D 2. I suggest to use banana leavesto wrap food. A B C D 3. Why don,t we used buses instead of motorbikes to avoid traffic jams. A B C D 4. How aboutreduced the amount of garbage we produce ? A B C D 5. Ithink that we should turned off the faucet . A B C D 6. The principal wants us pay more attention to our study. A B C D 7. Students stoppedto make noise when the teacher came in. A B C D 8. Would you mindto turning off the radio? A B C D 9. My parents decided take a taxi because it was too late. A B C D 10. All of us are very fond of read books after school. A B C D 11. They don’t like go to the zoo because they hate animals. A B C D 12. My told me signing a paper admittig his guilt. A B C D 13. The children are strong enoughcarry that heavy bag from the park to their house. A B C D 14. Could you to help me open this door? A B C D 15. The teacher asked us writing the exercises carefully. A B C D 16. He is interested in playsports. A B C D 17. You will be abledoing it yourself when you are older. A B C D 18. Some students avoid to look at the teacher if they don’t want to answer a question A B C D 19. She prefersdoing homework tohang out with friends. A B C D 20. Finally, they finishedto complete their tests. A B C D

2018 © Loga - Không Ngừng Sáng Tạo - Bùng Cháy Đam Mê
Loga Team