题目

（2011四川泸州，25，7分）如图，一艘船以每小时60海里的速度自A向正北方向航行，船在A处时，灯塔S在船的北偏东30°，航行1小时后到B处，此时灯塔S在船的北偏东75°，（运算结果保留根号）（1）求船在B处时与灯塔S的距离；（2）若船从B处继续向正北方向航行，问经过多长时间船与灯塔S的距离最近． 答案：解：（1）延长AB，作SC⊥AC，垂足为C．设SC=x．在Rt△ASC中，AC=xcot30°= x；在Rt△BSC中，BC=xcot75°=（2-）x．∵AB=60海里，又∵AB=AC-BC= 3x－（2－）x=（2－2）x，∴（2-2）x=60，解得：x=15（+1）海里．BS= xsin75°=30海里．故（1）BS=30海里；（2）船与灯塔S的最近距离为CS，船的航行时间为小时．解析:略7、Life in Senior 3 is both tiring, exciting and meaningful.  As it is known to us, it is far from relaxing and easy. 76. ___________  Every minute counts. Working late into night is often the 77. ___________  case. There is much homework or we have to take many 78. ___________  exams. Morever, we are sure to go across 79. ___________  and overcome a lot of difficulties in my studies. We 80. ___________  have made constant and great progress under the help 81. ___________  of the teachers. Besides our lessons, we also manage 82. ___________  to make fully use of free time to relax ourselves, girls reading 83. ___________  colorful magazines and boys play basketball. Busy and 84. ___________  tiring as we are, we still feel happy and confident of our future. 85. ___________