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已知某品牌手机公司生产某款手机的年固定成本为40万美元,每生产1万部还需另投入16万美元.设公司一年内共生产该款手机x万部并全部销售完,每万部的销售收入为R(x)万美元,且R(x)= {4006x,0<x408000
x
57600
x
2
,x>40
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同类题4

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         (核心提示:中国驻美大使崔天凯4月30日警告美国,勿卷入中日钓鱼岛纷争,“不要让日本这块石头砸了自己的脚”。)
         【环球时报综合报道】“不要让日本这块石头砸了自己的脚”,中国驻美大使崔天凯4月30日警告美国。这番罕见严厉的表态针对的是美国防长哈格尔,因为他近日不仅承认日本对钓鱼岛的管辖权,还扬言 “反对任何损害日本管辖权的单边行动”。
         日本防务省官员兴奋地称,哈格尔的说法 “比想像中对中国的警告还要更加强有力”。近期,不少美国官员在东亚穿梭,传递出的信息格外混乱,有说警告日本的,也有说遏制中国的,有官方背景的“美国之音”4月30日的评论像是定下一个基调——美国防、外交高层向中方传达一致立场,反对任何旨在破坏日本管辖权的单方面或强制行动。
        标榜在钓鱼岛问题上“中立”的美国态度开始明朗化,更多地为日本撑腰打气,这给本来就紧张的东亚增添新的复杂变数。美国《福布斯》杂志评论,美日同盟不可能保证钓鱼岛争端的局势不变,美国在某些时候必须避免因此与中国发生冲突。中国国际问题研究所学者阮宗泽5月1日对《环球时报》说,安倍晋三的右翼做派已经一览无余,美国如果一味放任日本,最后恐怕要自讨苦吃。

同类题5

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    Chokwe Selassie, aged 13, is working hard to help drivers avoid potholes(坑洼). The eighth-grader was inspired to kick off his creation on a recent morning, when his mother was driving him to school. Their car was damaged as it went over a huge pothole in the middle of the street in their hometown of Jackson, Mississippi. He decided to do something about the pothole problem in his city. His solution: an app that warns drivers when there is a pothole ahead.

    Chokwe developed the app with his friends Rodriguez Ratliff and Emmanuel Brooks. When the app detects a pothole, it is highlighted in red. And if you get close to the pothole, your phone will warn you. Drivers can also use the app to report any potholes they meet, and to look for other routes they can take to avoid roads that have them.

    The app relies on current available information about the streets of Jackson. It works by using the city's 311 call system, and uses information already stored in a database. Through the call system, citizens dial 311 to report non-emergency problems, which include potholes. Chokwe and his friends determined that focusing on the 10 busiest streets in Jackson would give them a large enough sample size to test the prototype(原型).

    Although the app isn't yet available for sale,Chokwe is already looking for ways to improve it. The prototype remains limited to 10 streets in Jackson, but he hopes to add more, so that it includes every street in the city. And then he wants to go even farther until it's nationwide.