随笔分类 -  BBC ENGLISH

摘要：http://weaman.blog.hexun.com/8319817_d.html 行列式是解线性方程组的有力工具。但是，行列式的展开，对于二阶、三阶行列式来说还比较方便，而对于高于三阶行列式的展开，则没有一般规律可循。这时，把高阶行列式降阶，使它转化为较低阶的行列式，则是一条可行的道路。“余子式”和“代数余子式”就是适应这种需要而产生的。 把行列式中某一元素所在的行与列划去后，剩下的元素按行列顺序排列所组成的行列式，叫做原行列式中对应于这个元素的余子式。 设行列式中某一元素位于第i行第j列，把对应于这个元素的余子式乘上(-1)i+j后，所得到的式子叫做原行列式中对应于这个元... 阅读全文

摘要：General Assembly passes resolution on Syria as deaths mountFrom the CNN Wire StaffFebruary 17, 2012 -- Updated 0325 GMT (1125 HKT)'Dire conditions' in SyriaSTORY HIGHLIGHTSVote was 137 in favor and 12 against in nonbinding measureU.N. focuses on humanitarian access, General Assembly resoluti 阅读全文

摘要：NEW YORK (AP) — Stocks slumped Wednesday in one of their worst showings this year as Greece, slogging through negotiations with other countries over a bailout, once again cast a long shadow over the financial markets.TheDow Jones industrial averagedropped 97.33 points to close at 12,780.95. It was t 阅读全文

摘要：OKUMA, Japan (Reuters) - Back home for just three hours, a tearfulMiyoko Takedasorted through her belongings. She left behind the kimonos she once wore as a traditional dancer, fearful they might be contaminated by radiation.Nearly a year has passed since a massive 9.0magnitude earthquakehitJapan, O 阅读全文