问题(人教版八年级上册)A和B两地在一条河的两岸,现要在河上造一座桥MN.桥造在何处可使从A到B的路径AMNB最短?(假定河的两岸是平行的直线,桥要与河垂直.)%A B N M图1b a教科书的分析是:把河的两岸看成两条平行线a和b(图1),N为直线b上的一个动点,MN垂直于直线b,交直线a于点M.这样,上面的问题可以转化为:当点N在直线b的什 A and B on both sides of a river, it is time to build a bridge on the river MN. Where does the bridge make the shortest path from A to B AMNB? (Assuming the two sides of the river Is a straight line parallel to the river, with the bridge perpendicular to the river.)% ABNM Figure 1b The textbook analysis shows the two banks of the river as two parallel lines a and b (Figure 1), N as a moving point on line b, MN perpendicular to the straight line b, cross a straight line at point M. Thus, the above problem can be transformed into: When the point N in the straight line b