user-avatar
whis605
2 năm trước
Cho ∆ABC vuông tại A vẽ đường cao AH có AB = 6cm, AC = 8cm. a) Chứng ∆HBA đồng dạng với ∆ABC; b) Tính BC, AH, HC; c) Chứng minh AH^ = HB.HC d)gọi i và k lần lượt là hình chiếu của h lên cạnh ab và ac CM ai.ab=ak.ac
Thích Trả lời Chia sẻ

Các câu hỏi liên quan

36. On July 20th, 1969, Astronaut Neil Armstrong_________ down onto the moon, the first person ever to set foot on another celestial body. A. Was stepping B. stepped C. has stepped D. was step 37. The plane's departure was delayed because of mechanical difficulties. When the weary passengers finally boarded the aircraft, many were annoyed and irritable because they___________ in the airport for three and a half hours. A. Are waiting B. were waiting C. have been waiting D. had been waiting 38. If coastal erosion continues to take place at the present rate in another fifty years, this beach_______anymore. A. Doesn't exist B. isn't going to exist C. isn't existing D. won't be existing 39. Homestead High School's football team_______a championship until last season, when the new coach led them to take first place in their league. A. Has never won B. is never winning C. had never been winning D. had never won 40. To be able to qualify as an interpreter, many years of intensive language study are required for non-native speakers. By the end of this year, Chen________English for three years, but he will still need more training and experience before he masters the language. A. Will be studying B. has studied C. will have been studying D. has been studying 41. In our hospital, patients________ every morning. A. Are examined B. have examined C. can examine D. were examining 42. I_________ in Can Tho for 18 years, but now I'm living in Ho Chi Minh city. A. Have lived B. live C. lived D. have been living 43. I wondered why he_________ his job. A. Has changed B. changes C. used to change D. had changed 44. The department store__________ by the Johnson for many years. A. Has been run B. is run C. runs D. has run 45. Kate________ 10 comedies this summer. A. Has watched B. had watched C. will have watched D. watched 46. The number of footballers________ for the last ten years. A. Has increased B. was increasing C. have increased D. were increasing 47. Don't worry! We_______for you at 6 o'clock tomorrow. A. Will wait B. will be waiting C. wait D. are waiting 48. Mary__________the country by the time this letter reaches her. A. Is going to leave B. will leave C. is leaving D. will have left 49. By this time next year, my father________here for 25 years. A. Are going to work B. will be working C. will have been working D. will work 50. Tim_________in three movies already. I think he'll be a star some day. A. Had appeared B. has appeared C. was appearing D. is appearing 51. They_________the door. No one can get in now. A. Have locked B. had locked C. locked D. lock 52. The existence of many stars in the sky__________ us to suspect that there may be life on another planet. A. Have led B. leads C. lead D. leading 53. They___________ the town hall for the past three years in fact, but they it yet. A. Built/ hadn't finished B. had built/ didn't finish C. have been building/ haven't finished D. have built/ weren't finishing 54. When I met Jim, he__________ from his university already. A. Graduated B. has graduated C. had graduated D. was graduating

21. "Hurry up! We're waiting for you. What's taking you so long?" "I________ for an important phone call. Go ahead and leave without me." A. Wait B. will wait C. am waiting D. have waited 22. Robert is going to be famous some day. He_________in three movies already. ~ I'm sure he'll be a star. A. Has been appearing B. had appeared C. has appeared D. appeared 23. Where's Polly? ~She_________. A. Is in her room studying B. in her room is studying C. studies in her room D. has in her room studied 24. Hello? Alice? This is Jeff. How are you? ~ Jeff? What a coincidence! I_________ about you when the phone rang. A. Was just thinking B. just thought C. have just been thinking D. was just thought 25. What___________ about the new simplified tax? ~It's more confusing than the old one. A. Are you thinking B. do you think C. have you thought D. have you been thinking 26. When is Mr. Fields planning to retire? ~ Soon, I think. He________ here for a long time. He'll probably retire next year or the year after that. A. Worked B. had been working C. has been working D. is working 27. Why did you buy all this sugar and chocolate? ~ I_________a delicious dessert for dinner tonight. A. Make B. will make C. am going to make D. will have made 28. Let's go! What's taking you so long? ~ I'll be there as soon as I__________my keys. A. Found B. will find C. find D. am finding 29. Next week when there______ a full moon, the ocean tides sill be higher. A. Is being B. is C. will be D. will have been 30. While I______TV last night, a mouse ran across the floor. A. Watch B. watched C. was watching D. am watching 31. Fish were among the earliest forms of life. Fish__________ on earth for ages and ages. A. Existed B. are existing C. exist D. have existed 32. The phone ________constantly since Jack announced his candidacy for president this morning. A. Has been ringing B. rang C. had rung D. had been ringing 33. The earth_________on the sun for its heat and light. A. Is depend B. depending C. has depended D. depends 34. I don't feel good. I________ home from work tomorrow. A. Am staying B. stay C. will have stayed D. stayed 35. Today there are weather satellites that beam down information about the earth's atmosphere. In the last two decades, space exploration_________ great contributions to weather forecasting. A. Is making B. has made C. made D. makes

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