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Tìm giá trị nhỏ nhất (lớn nhất) của biểu thức: a) x² -2x + 10 b) x² - x + 1 c) 2x - x² + 5 d) 3x - x² e) x² + 4y² - 2x + 4y + 5 f) x² - x + y² + y - 2
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Read the following passage and choose the best answer (A, B, C or D) to each question. A geyser is the result of underground water under the combined conditions of high temperatures and increased pressure beneath the surface of the Earth. Since temperature rises about 1°F for every sixty feet under the Earth surface, and pressure increases with depth, water that seeps down in cracks and fissures until it reaches very hot rocks in the Earth's interior becomes heated to temperature of approximately 290°F.Water under pressure can remain liquid at temperatures above its normal boiling point, but in a geyser, the weight of the water nearer the surface exerts so much pressure on the deeper water that the water at the bottom of the geyser reaches much higher temperatures than does the water at the top of the geyser. As the deep water becomes hotter and consequently lighter, it suddenly rises to the surface and shoots out of the surface in the form of steam and hot water. In turn, the explosion agitates all the water in the geyser reservoir, creating further explosions. Immediately afterward, the water again flows into the underground reservoir, heating begins and the process repeats itself. In order to function, then, a geyser must have a source of heat, a reservoir where water can be stored until the temperature rises to an unstable point, an opening through which the hot water and steam can escape, and underground channels for resupplying water after an eruption. Favourable conditions for geysers exist in regions of geologically recent volcanic activity, especially in areas of more than average precipitation. For the most part, geysers are located in three regions of the world: New Zealand, Iceland, and the Yellow National Park area of the United States. The most famous geyser in the world is Old Faithful in Yellowstone Park. Old Faithful erupts every hour, rising to a height of 125 to 170 feet and expelling more than ten thousand gallons during each eruption. Old Faithful earns its name because, unlike most geysers, it has never failed to erupt on schedule even once in eighty years of observation. 1. Which of the following is the main topic of the passage? A. The Old Faithful geyser in Yellowstone National Park B. The nature of geysers C. The ratio of temperature to pressure in underground water D. Regions of geologically recent volcanic activity 2. In order for a geyser to erupt, _____. A. hot rocks must rise to the surface of the Earth B. water must flow underground C. it must be a warm day D. the Earth must not be rugged or broken 3. The word „it‟ in line 4 refers to _____. A. water B. depth C. pressure D. surface 4. As depth increases _____. A. pressure increases but temperature does not B. temperature increases but pressure does not C. both pressure and temperature increase D. neither pressure nor temperature increases 5. Why does the author mention New Zealand and Iceland in paragraph 4? A. To compare areas of high volcanic activity. B. To describe the Yellowstone National Park. C. To provide examples of areas where geysers are located. D. To name the two regions where all geysers are found. 6. How often does Old Faithful erupt? A. Every 10 minutes B. Every 60 minutes. C. Every 125 minutes. D. Every 170 minutes. 7. The word „expelling‟ in paragraph 4 is closest in meaning to _____. A. heating B. discharging C. supplying D. wasting 8. What does the author mean by the statement: “Old Faithful earns its name because, unlike most geysers, it has never failed to erupt on schedule even once in eighty years of observation.”? A. Old Faithful always erupts on schedule. B. Old Faithful is usually predictable. C. Old Faithful erupts predictably like any other geysers. D. Old Faithful received its name because it has been observed for many years. 9. The word „precipitation’ in paragraph 4 is closest in meaning to _____. A. the amount of steam B. the amount of rain C. humidity D. heat 10. According to the passage, what is required for a geyser to function? A. A source of heat, a place for water to collect, an opening, and underground channels. B. A source of heat, an active volcano nearby and a water reservoir. C. Channels in the Earth, heat and heavy rainfall and water underground. D. Volcanic activity, underground channels and steam.

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