Cho biểu thức A =

a)Đặt điều kiện để biểu thức A có nghĩa;       b)Rút gọn biểu thức A;

c)Với giá trị nào của x thì A< -1.

Bài 4: cho tam giác ABC vuông tại A, đường cao AH.  Kẻ HI vuông góc với AB tại I, kẻ HK vuông góc với AC tại K.

a/ tứ giác AIHK là hình gì? Vì sao?

b/ tính IK

c/ chứng minh AI.AB=AK.AC

Use the words to write the second sentence in such a way that it is as similar as possible in

     meaning to the original sentence. Do not change the form of the given words. 

1. I’m not you, but I think you should recycle these plastic carrier bags. (if)

………………………………………………………………………………………………..

2. Emma came first because she worked hard. (result)

……………………………………………………………………………………………….

3. Eating too much sugar can result in health problems. (lead)

………………………………………………………………………………………...……..

4. All flights had to be cancelled as a result of the pilots’ sudden strike. (so)

………………………………………………………………………………………….……

5. If I could swim, I would go scuba diving with Terry. (because)

……………………………………………………………………………………………….

Complete the second sentence in such a way that it is almost the same meaning as the first, using the word given. 

1.The match couldn’t start because of the heavy snow.

->The heavy snow……………………………………………………………….….

2. My mother was a worker in a factory when she was young.

         -> My mother used…………………………………………………………………...

3.You can improve your English by practicing speaking every day.

            -> If…………………………………………………………………………………

4.  “ I really must leave now,”  Mr. Fatt said.

            -> Mr. Fatt insists……………………………………………………………….…..

5. It often took my mom half an hour to get to work by underground every morning last month.

            -> My mom spent…………………………………………………………………….

…… (1) ... six o’clock yesterday evening, the River Thames burst its banks and flooded a wide area. By nine o’clock the floods had reached the town of Dorchester. The main street was soon …… (2)..... 3 feet of water. Fire engines arrived quickly to pump away the water, but heavy rain made their job very ……… (3) ..... .

Mrs Rose Willow, a ……… (4)......... nearly 80 years old, and living alone in her cottage, was trapped upstairs ……… (5)........ three hours. Finally, firemen were able to rescue her with ladders and a small ……… (6).......... “My cat, Tibbles, stayed with me all the time”, said Mrs Willow. “She ……… (7)......... me a lot. She sat with me so I didn’t feel afraid”.

The rain has finally stopped, the river level is falling and the weather forecast is good, ……… (8) ...........the floods have done a great deal of damage. “Luckily, nobody was …… (9) ......or injured”, Chief Fire Office Hawkins …… (10) .......reporters, “but it will take a long time to clear up the mess”.