Cho đường tròn (O;R) đường kính AB cố định. Điểm I nằm giữa A và O. Dây CD vuông góc AB tại I. Gọi M là điểm tuỳ ý thuộc cung lớn CD (M không trùng với C,D,B). Dây AM cắt CD tại K

1) Cm tứ giác IKMB nội tiếp

2) Cm AD^2=AK.AM

3) Cm AC là tiếp tuyến của đường tròn tâm E ngoại tiếp tam giác CKM

4) Xác định vị trí của điểm M sao cho độ dài DE nhỏ nhất

* Mọi người giúp mình câu 3) với 4) thôi nhé, mấy câu kia mình làm được rùi. Thanks trước nà :3

I. Active or passive

1. Seventy-five prisoners in northern Mexico..........(spend) over six montha digging a tunnel in an attempt to escape form Satillo prison. Unluckily for them, thier tunnel.........(come) up in the nearly courtroom, where they.........(sentence). All 75 prisoners.........(return) to prison immediately.

2. Mrs.Redwood, from Port Headland,.........(attack) by a burglar while she.......(talk) on the phone to her brother in Leeds. Her brother........(hear) strange noises, and,......(phone) his local office station in Leeds. The Port Headland police.........(contact) immediately, and an officer........(send) to Mrs.Redwood’s house. The woman.........(rescue) just eighteen minutes after the attack.........(happen).

3. A towel..........(steal) from a “Holiday Inn” hotel in the US every 12 seconds.

II. Use the correct forms of thr verbs in the brackets

The custom officer was suspicious when the man........(appear) at the border crossing. He made the man.........(open) his suitcase, but there was noting valuable in it. So the officer het him........(cross) the border. Every week after that the same thing........(happen). The man.........(arrive) and the officer.........(stop) him and........(search) his suitcase. Sometimes he made the man.........(wait) for some hours. He was sure that the man..........(smuggle) something but he...........(never/find) anything. The the day came when the customs officer retired, and he.........(decide) that before he..........(leave), he would get the man.........(tell) the truth. So he got another customs officer..........(stop) the man and had him.........(bring) to the office. “I........(retire) tomorrow”, he said. “I know that you........(smuggle) all those years. Please tell me what it is. You have my word that I..........(not/tell) anyone.” The man.........(look) at him, smiled and..........(say):”Suitcases.”

III. Passive or active

1. These days, even the most remote place on earth........(visit) by tourists. Package tours.........(can/arrange) for almost anywhere, from the Himalayas to the Amazonian jungle.

2. Notices such as English Spoken or Shoes Repaired are common. Sometimes they........(translate) in different languages for the benefits of tourists.

3. We........(constantly/remind) of the way the world........(become) smaller.

4. If you are involved in a car accident and someone.........(hurt), you.........(have to) report the matter to the police.

5. More cars.........(steal) every year in Britain than in any other European country.

Áp dụng bất đẳng thức cô-si tìm max

a) A=-x^2+2x+7

b) B=(x-y)(5-2x+2y)+14

Giúp mình nha!!!!