一天24小时内分为以12小时为一圈的两个周期.设时针的角度v,则分针的角度为12v,秒针的角度为144v.三者重合时分针转了k圈,秒针转了X圈,列方程式如下: v/2π=(12v-2kπ)/2π v/2π=(144v-2Xπ)/2π v<2π,0<=v<2π或0<v<=2π 解得v=0或v=2π
北京到广州的距离。
设北京到广州的距离为A,则两辆火车相遇需要
A/(15+20)小时,也就是说鸟儿飞了A/(15+20)小时,时间乘以速度等于它飞的距离,30*A/35=6/7A
DOM is a platform-and language-neutral API that allows programs and scripts to dynamically access and update the content ,structure and style of WWW documents (currently,definitions for HTML and XML documents are part of the specification).The document can be further processed and the results of that processing can be incorporporated back into the presented page. DOM is a tree-based API to document ,which requires the whole document to be represented in_memory while processing it .A simpler alternative to Dom is the event-based SAX,which can be used to process very large XML documents that do not fit into the memory available for processing. |