Cho $a;b>0.$ Chứng minh: \[\dfrac 1a+\dfrac 1b\ge \dfrac{4}{a+b}\]

1. A visit B. travel C. turn D. come 2.A. tell B. say C. report D. explain 3.A. tell B. say C. research D. convince 4.A. take B. make C. get D. go. 5.A. felt B. feel C. feeling D. feels 6.A. try B. begin C. help D. never 7.A. cure B. treat C. research D. fight 8.A. about B. for C. to D. from 9.A. beat B. took C. defeated D. won 10.A. locking B. putting C. endangering D. limiting B. Read the passage then choose the most suitable answer for each question(1 point) The search for alternative sources of energy has led in various directions. Many communities are burning garbage and other biological waste products to produce electricity. Converting waste products to gases or oil is also an effective way to dispose of wastes. Experimental work is being done to derive synthetic fuels from coal, oil shale, and coal tars. But to date, that process has proven expensive. Other experiments are underway to harness power with giant windmills. Geothermal power, heat from the Earth, is also being tested. Some experts expect utility companies to revive hydroelectric power derived from streams and rivers. Fifty years ago hydro-electric power provided one-third of the electricity used in the United States, but today it supplies only 4 percent. The oceans are another potential source of energy. Scientists are studying ways to convert the energy of ocean currents, tides, and waves to electricity. Experiments are also underway to make use of temperature differences in ocean water to produce energy. 1. Which is the best title for the passage? A. The use of Water products for energy B. The search for Alternative sources of Energy. C. Efficient ways of disposing of waste D. New discoveries in Geothermal power. 2. Fifty years ago one-third of the electricity in the United States was provided by______. A. wind B. water products C. water D. oil 3. In the second paragraph, the phrase “Synthetic fuels” could best be replaced by which of the following______. A. biological fuels B. low burning fuels C. fast burning fuels D. artificial made fuels. 4. Which of the following is not mentioned in the passage as an alternative source of energy? A. Burning of garbage B. Geothermal power C. Synthetic fuels D. Electricity. 5. According to the author, the impracticability of using coal, oil shale and coal tars as source of energy is due to______. A. their being time consuming B. their being money consuming C. the scarcity of sources D. the lack of technology

Ai giải giúp em hết tờ toán này với em chỉ còn mỗi 10 điểm thôi em cảm ơn

Giải giúp mình câu 1 và câu 2 dưới đây vs ạ

Giai phương trình sau 4/2x-3-7/3x-5=0 4/(2x-3) + 4x/(4x^2-9)=1/2x+3

Cho đường tròn (O) đường kính bằng 8cm và điểm A sao cho OA = 8cm. Vẽ tiếp tuyến AB với đường tròn (O) (B là tiếp điểm). Vẽ dây BC vuônng góc với OA tại I. a) Tính độ dài AB, BI. b) Chứng minh rằng: AC là tiếp tuyến của đường tròn (O). c) Đoạn OA cắt đường tròn (O) tại M. Qua M vẽ tiếp tuyến với đường tròn (O), tiếp tuyến này cắt AB và AC lần lượt tại D và E. Tính số đo DOE

17. You_______ walk on the ice. A. mustn't B. needn't C. mightn't D. shouldn't 18. At one time the entire world_______ by dinosaur. A. was ruled B. were ruling C. has ruled D. will be ruled 19.He warned me_______ late-night horror film. A. not watch B. against watching C. not watching D. about to watch 20.It's a about time we_______ rid of this old car. A. get B. will get C. has got D. got 21. My family_______ go to Samson beach in summer when we lived in Thanh Hoa. A. use B. used C. used to D. are used to 22.Our home needs_______. A. Painting B.to paint C. be painted D. paint 23.He often goes to the_______ to pray because his religion is Islam. A. temple B. mosque C.church D. pagoda 24.If we_______ wasting our natural resources, they will be used up in a few decade. A. turn on B. go on C. go off D. turn off 25. _______ there have been many changes in our country, it still remains a developing one. A. however B. despite C. because D. although B. Write the correct form of the word in the blank. (1.5 points) 1.News on TV is very ...................... (Inform) 2.He gets bad grades because of his................... (Lazily) 3.What is his ............................? (Nation) 4.Every man loves ................................ beauty. (Nature) 5.She had a lot of ............................ for Tet. (Prepare) 6.He run very..............……….……… (Quick) 7.It is cloudy and .......................... toay. (Rain) 8.We are interested in .......................... books. (Read) 9.Ha Long Bay is one of the ........................... of the world. (Wonderfully) 10.This…………has written many stories for children. (Write) c. Find the word(s) marked A, B, C or D that is incorrect in each of the following sentences then correct it.(1 point) 1.He should ever call again, please tell him that I am not at home. A B C D 2.She did not know where most of the people in the room was from. A B C D 3.It is impossible to believe that somebody actually admire that man. A B C D 4.According to the syllabus, you can either write a paper or you can take an exam. A B C D 5.Florida has become the twenty-seventh state in the United States on March 3, 1845. A B C D III. Reading comprehension(2 points) A. Read the passage then choose one suitable answer from the four options to fill each blank. No matter where you(1)______ in the world, there is one language that everyone understand: laughter. Scientists (2)______ us that laughter is good for us. They (3)______ that laughter can actually help us to (4)______ rid of pain and make us (5)______ good. Some scientists also say that laughter can (6)______ kill viruses and even help the (7)______ against cancer. You may have heard (8) the author who says he fought and (9)______ a battle with cancer by (10)______ himself in a room for hours to watch funny videos.

một xe đạp khởi hành từ điểm A với vận tốc 35km/h. sau 6 giờ một xe hơi đuổi theo với vận tốc 60km/ h. Hỏi xe hơi chạy trong bao lâu thì đuổi kịp xe đạp? Giúp mình với Giải bài toán bằng cách lập phương trình nha

Thực hiện phép tính (-5)^2.(-3)^2.2^3

a,|x-3|-16=-4. b,26-|x+9|=-13