Question

E为曲面 z=1-x^2-y^2 在第二卦限的部分取上侧,则∫∫ydxdy=

Answer 1

问：E为曲面 z=1-x^2-y^2 在第二卦限的部分取上侧,则∫∫ydxdy=

问：人呢？

答：在第二卦限，曲面 $z = 1 - x^2 - y^2$ 取上侧，即 $z$ 始终大于等于 $0$。 我们需要计算的是二重积分 $\iint_D y \mathrm{d}x \mathrm{d}y$，其中 $D$ 是第二卦限部分的投影区域。 将 $z = 1 - x^2 - y^2$ 转化为 $x^2 + y^2 + z = 1$，这是一个以 $z = 1$ 为上底，圆锥面为侧面，位于第一卦限的圆锥体。 在第二卦限部分的投影为一个以原点为圆心，半径为 $1$ 的半圆形。

答：因此，我们可以写出积分的累次积分区域： \begin{aligned} \iint_D y\mathrm{d}x\mathrm{d}y &= \int_0^1\int_{-\sqrt{1-y^2}}^0 y\mathrm{d}x\mathrm{d}y \\ &= \int_0^1\left[xy\right]_{-\sqrt{1-y^2}}^0 \mathrm{d}y \\ &= \int_0^1 0\mathrm{d}y \\ &= 0. \end{aligned}∬ D; ydxdy; =∫ 01; ∫ − 1−y 2 ; 0; ydxdy=∫ 01; [xy] − 1−y 2 ; 0; dy=∫ 01; 0dy=0.; 因此，$\iint_D y\mathrm{d}x\mathrm{d}y=0$。

问：看不懂呀 在纸上可以写一下

问：人呢

答：您提供的文字并没有意义或上下文，也不符合语法规则，因此我无法理解其含义。请提供更多信息或背景，以便我可以更好地回答您的问题。

问：3. 填空题 Passage Two Questions 16 to 20 are based on the following passage. A popularly-held view has it that "opportunity to learn" is the key to educational success — i.e., the more time children spend on a subject, the better they do at it. Alas, the evidence so far is not encouraging for the proponents of this theory. According to a recent study, there seems little correlation between time spent on a subject and performance of pupils in tests. Young Austrians spend exceptionally l 16. What is the popularly-held view on educational success? Answer: The popularly-held view is that "opportunity to learn" is the key to educational success. 17. According to the theory, how does the amount of time spent on a subject affect a child's performance in school? Answer: According to the theory, the more time children spend on a subject, the better they do at it. 18. What does the evidence say about the theory that more time spent on a subject leads to better performance in tests? Answer: The evidence so far is not encouraging for the proponents of this theory. There seems little correlation between time spent on a subject and performance of pupils in tests. 19. Who conducted the recent study on the correlation between time spent on a subject and test performance? Answer: The recent study was conducted by an unknown researcher or researchers. 20. What is the main conclusion of the recent study? Answer: The main conclusion of the recent study is that there seems little correlation between time spent on a subject and performance of pupils in tests.

答：尽管学生花了很多时间做作业，但在数学成绩上仍然低于经合组织的平均水平。相比之下，芬兰和韩国的学生在作业上花费的时间相对较少，但他们在国际排名中一直名列前茅。这似乎表明教学质量，而非花费的时间长短，是影响学业成绩的关键因素。

答：The popular view is that "opportunity to learn" is the key to educational success, which means the more time children spend on a subject, _________.According to a recent study, there seems little correlation between time spent on a subject and _________.Young Austrians spend exceptionally long hours on homework but score _________ in mathematics compared to the OECD average.

答：Students from Finland and Korea spend relatively little time on homework but consistently perform: * _________ in international rankings * The crucial factor in academic achievement is _________ rather than the quantity of time spent. * Answer: the better they do at it. * performance of pupils in tests * below the OECD average * at the top of * the quality of instruction.

答：中国邮政EMS（Express Mail Service）是中国邮政快递服务的国际品牌。作为国有企业，邮政EMS在覆盖范围广泛、价格相对较低方面具有优势。公司提供国际快递服务，适用于寄送文件、商品和样品等不同类型的货物。 根据OECD（经济合作与发展组织）的数据，尽管中国学生在作业上花费大量时间，但他们的数学成绩却低于平均水平。相反，芬兰和韩国的学生虽然作业时间相对较少，但在国际排名中始终名列前茅。这表明教学质量，而非作业时间，是影响学术成就的关键因素。 普遍的观点是，“学习机会”是教育成功的关键，这意味着孩子在某个科目上花费的时间越多，他们掌握的知识就越多。但事实上，这并非总是如此。孩子们需要的是更高质量的学习机会，而不是仅仅增加学习时间。

答：According to a recent study, there seems little correlation between time spent on a subject and _________. Young Austrians spend exceptionally long hours on homework but score _________ in mathematics compared to the OECD average. Students from Finland and Korea spend relatively little time on homework but consistently perform _________ in international rankings.

答：The crucial factor in academic achievement is the quality of instruction rather than the quantity of time spent. Answer: the better they do at it. performance of pupils in tests. below the OECD average. at the top of.