Cho tam giác abc cân tại a có ac=10cm,bc=12cm. Kẻ ah vuông góc bc tại h A) c/m hb=hc B) tính độ dài ah C( kẻ hi vuông goc ab tại i,hk vuông góc với ac tại k. C/m tam giác hik cân D) c/m ik//bc

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ndduc2001 giúp mình giải 3 bài này với nhé 1/Cho cơ hệ như hình 3.24. Biết m1 = 2 kg, m2 = 6 kg; θ= 45 độ. Bỏ qua ma sát ở trục ròng rọc, khối lượng dây và ròng rọc không đáng kể; coi dây không giãn. Giữa vật m2 và mặt phẳng nghiêng không có ma sát. Lấy g = 10 m/s2. a. Xác định gia tốc chuyển động của các vật ? b. Tính áp lực tác dụng lên ròng rọc? c. Xác định vận tốc mỗi vật sau 2.00s từ khi mỗi vật được giải 2/Một hộp nhôm khối lượng m1=2.00kg và một hộp đồng khối lượng m2=6.00kg được nối với nhau bằng một sợi dây nhẹ vắt qua ròng rọc nhẹ không ma sát . Hệ được đặt trên một bề mặt có góc nghiêng θ=30 độ như hình 3.27 a. Xác định gia tốc các vật nếu khi thả hệ, các vật bắt đầu chuyển động trên bề mặt hoàn toàn nhẵn? b. Nếu giữa hai vật và mặt phẳng có ma sát, hệ số ma sát trượt bằng 0,2. Xác định gia tốc của các vật? 3/Khi hai vật có khối lượng m1=2kg và m2=7kg nối với nhau bằng một dây nhẹ, không giãn, được treo thẳng đứng trên một ròng rọc nhẹ và không có ma sát ở trục Truyền vận tốc tức thời 2.40m/s vào vật có khối lượng nhỏ hơn theo phương thẳng đứng hướng xuống. như hình 3.30 a. Hãy tìm quãng đường vật m1 đi được so với vị trí ban đầu được truyền vận tốc. b. Vận tốc của vật m1 sau khi chuyển động được 1.80s.

Choose the best answer a, b, c or d to complete the sentence. Question 5. How much time do you spend _______ leisure activities? A: on B: with C: for D: in 21 Read the passage carefully, then choose the correct answers. The latest addiction to trap thousands of people is the Internet, which has been blamed for broken relationships, job losses, financial ruin, and even suicide. Psychologists now recognize Internet Addiction Syndrome (IAS) as a new illness that could cause serious problems and ruin many lives. IAS is similar to other problems like gambling, smoking and drinking: addicts have dreams about the Internet; they need to use it as the first thing in the morning; they lie to their parents and partners about how much time they spent online; they wish they could cut down, but are unable to do so. A recent study found that many users spend up to 40 hours a week on the Internet. Some of the addicts are teenagers who are already hooked on computer games and who find it very difficult to resist the games on the Internet. Which of the followings is NOT true? A: Internet addiction can cause suicide behaviors. B: IAS is recognized as a new illness. C: Teenagers who are hooked on computer games can suffer from IAS. D: Many Internet addicts spend more than 40 hours a week online. 22 Mark the letter A, B, C or D to indicate the most suitable response to complete each of the following exchanges. Question 13. Mary: “Would you like to join our volunteer group this summer?” Peter: “……………………………………….” A: Do you think I would? B: Yes, you are a good friend C: Thanh you so much! D: Yes, I’d love to. Thanks. 23 Mark the letter A, B, C or D to indicate the word(s) CLOSEST in meaning to the underlined word(s) in each of the following questions. Question 11. My mother usually spends her free time looking after her cats. A: taking after B: taking care of C: taking over D: looking at 24 Choose the word whose stressed pattern is pronounced differently from the others. A: addicted B: detest C: community D: leisure 25 Choose the sentence so that it has similar meaning to the first one. Question 24. How about going window-shopping this afternoon? A: Shall we go window-shopping this afternoon? B: What about to go window-shopping this afternoon? C: Shall we going window-shopping this afternoon? D: Will we go window-shopping this afternoon?

Choose the underlined part A, B, C or D that needs correcting. Picture 6 A: A B: B C: C D: D 10 Choose the best answer a, b, c or d to complete the sentence. Question 6. Daisy is _______ social media. She spends lots of time on Facebook and Instagram. A: bored with B: curious about C: addicted to D: tired of 11 Choose the word whose stressed pattern is pronounced differently from the others. A: adore B: event C: relax D: teenager 12 Choose the best answer a, b, c or d to complete the sentence. Question 8. My sister enjoys _______. She usually walks around the mall to look at the goods, but not buying anything. A: going shopping B: window shopping C: doing DIY D: hanging out 13 Read the passage carefully, then choose the correct answers. The latest addiction to trap thousands of people is the Internet, which has been blamed for broken relationships, job losses, financial ruin, and even suicide. Psychologists now recognize Internet Addiction Syndrome (IAS) as a new illness that could cause serious problems and ruin many lives. IAS is similar to other problems like gambling, smoking and drinking: addicts have dreams about the Internet; they need to use it as the first thing in the morning; they lie to their parents and partners about how much time they spent online; they wish they could cut down, but are unable to do so. A recent study found that many users spend up to 40 hours a week on the Internet. Some of the addicts are teenagers who are already hooked on computer games and who find it very difficult to resist the games on the Internet. According to the writer, Internet addiction __________. A: is not the same as gambling B: is not an illness C: can lead to financial problems D: helps people kill time 14 Choose the best answer a, b, c or d to complete the sentence. Question 9. You can raise a ______ pet like a Neopet if you aren’t allowed to own a real pet. A: virtual B: domestic C: beloved D: weird 15 Mark the letter A, B, C or D to indicate the most suitable response to complete each of the following exchanges. “My favorite leisure activity is people watching.” “_______” A: That’s all right. B: That sounds so weird! C: Sure. It’s very entertaining. D: OK. That’s very kind of you 16 Choose the sentence so that it has similar meaning to the first one. Question 23. What leisure activity does she like most? A: What activity does she like doing most? B: What does she like most? C: What’s leisure activity does she like most? D: What’s her favorite activity in her free time? 17 Choose the best answer a, b, c or d to complete the sentence. Question 10. My favorite hobby is ______. I spend most of my free time making vases and bowls from clay. A: bird watching B: woodcarving C: pottery making D: model making 18 Choose the word whose underlined part is pronounced differently from the others. A: hooked B: socialized C: satisfied D: bored 19 Mark the letter A, B, C or D to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions. Question 12. Do you adore skateboarding in the park this Sunday. A: fancy B: dislike C: enjoy D: love