请教QYQ中的一道题……

小腾

At 9 a.m,a hiker was due south of point P. What direction was point P from her position at noon?

(1)From 9 a.m until 11 a.m she walked due east at 2 miles per hour, and from 11 a.m until noon, she walked due north at 3 miles per hours.

(2)At noon,she is exactly 4.5 miles from point P

答案选的是E，为什么不是C呢？

goodfishs

因为P的位置不确定。你画个图看看。P和刚开始的点的距离可以大于1也可以小于1。

luoye1

这个题目相当的tricky.

从起点往东走了4 miles,往北走了3公里.

如果这点距离P 正好4.5公里,那么其实只有两种可能.

假设p为原点，那么终点的这两种可能是:

(4, ((4.5)^2-4^2)^(1/2)) 和(4, -((4.5)^2-4^2)^(1/2))

当然画图非常方便.

但我觉得，如果这个半径不是4.5, 比如说5, 那么这个题目答案是C.

请大侠指正!