综观全国各地中考试题,运用三角函数解决与直角三角形有关的简单实际问题是中考的必考内容,且大多数以“双直角三角形”的面孔出现,而双直角三角形问题可以看作由课本题变式而来的,若理解它们之间的内在联系,遇到此类问题就能举一反三,触类旁通,为帮助同学们掌握这类问题的变化规律,本文将结合课本例题加以分析,供学习时参考.课本原题(人教课标版教科书九年级下册第89页例题5)如图1,一艘海轮位于灯塔P的北偏东65°方向,距离灯塔80海里的A处,它沿正南方向航行 Looking at the middle school exam questions all over the country, the use of trigonometric functions to solve simple and practical problems related to right-angled triangles is the most important part of the exams. Most of them appear in the faces of “double right-angled triangles”, whereas the double- In order to help students master the changing law of such problems, this article will analyze the examples of textbooks for the purpose of learning when they encounter the problems of one kind or the other. Example 5) As shown in Figure 1, a seagoing vessel is located 65 ° north east of the Lighthouse P at a distance of 80 nautical miles from the lighthouse and along Is sailing south