题目

完形填空 Traveling in Vietnam was like visiting a mysterious neighbor. You have lived next door to each other for years but know very 1 about what happened on 2 side of the fence. I travelled there last August. A(n) 3 180-kilometre trip from a Chinese border town to Hanoi, the capital of Vietnam, 4 an adventurous eight hours. That's 5 the country still doesn't have a modern expressway system. The major passage going through the country is only a two-way road. 6, many areas are mountainous. Vietnamese drivers are 7 and fearless. They compete with each other at full speeds no matter how scar5．如图，二次函数y=ax2-2amx-3am2（其中a、m是常数，且a＞0，m＞0）的图象与x轴分别交于点A、B（点A位于点B的左侧），与y轴交于C（0，-3），点D在二次函数的图象上，CD∥AB，连接AD，过点A作射线AE交二次函数的图象于点E，AB平分∠DAE．（1）直接写出关于此函数图象的两条性质；（2）用含m的代数式表示a；（3）试求AD：AE的值；（4）设该二次函数图象的顶点为F，探索：在x轴的负半轴上是否存在点G，连接GF，以线段GF、AD、AE的长度为三边长的三角形是直角三角形？如果存在，只要找出一个满足要求的点G即可，并用含m的代数式表示该点的横坐标；如果不存在，请说明理由．