<p>解释起来比较麻烦,又没有办法贴图,不过这里有个网址讲的很详细</p><p>你去看一下行么</p><p><a href="http://books.google.cn/books?id=YG6b7zV8x2YC&pg=PA74&lpg=PA74&dq=%E8%BE%B9%E9%99%85%E7%A6%8F%E5%88%A9%E6%88%90%E6%9C%AC&source=web&ots=xra7wrJmro&sig=yWQW07V0HBGHzVGaRrFLufFfBAQ&hl=zh-CN&sa=X&oi=book_result&resnum=16&ct=result#PPA74,M1">http://books.google.cn/books?id=YG6b7zV8x2YC&pg=PA74&lpg=PA74&dq=%E8%BE%B9%E9%99%85%E7%A6%8F%E5%88%A9%E6%88%90%E6%9C%AC&source=web&ots=xra7wrJmro&sig=yWQW07V0HBGHzVGaRrFLufFfBAQ&hl=zh-CN&sa=X&oi=book_result&resnum=16&ct=result#PPA74,M1</a></p>