题目

VISIONS Service Adventures Since 1989, VISIONS has organized community service summer programs for teens. Live with other teens in a neighborhood of our host community; be more than a tourist. High school students on the VISIONS Alaska community service program will earn 100 service hours doing meaningful summer projects including environmental work and social services. You will also experience amazing Alaska adventures such as backpacking climbing and more. PROGRAM DATES July 3 to July 28 OUR HOME BASETetlin Village, a native village with rich traditions. Student volunteers on the VISIO如图1，在平面直角坐标系中，AB、CD都垂直于x轴，垂足分别为B、D，AD与BC相交于E点，已知：A（-2，-6），C（1，-3），一抛物线经过A，E，C三点．（1）求点E的坐标及此抛物线的表达式；（2）如图2，如果AB位置不变，将DC向右平移k（k＞0）个单位，求△AEC的面积S关于k的函数表达式；（3）在第（2）问中，是否存在k的值，使AD⊥BC？如果存在，求出k的值；如果不存在，请说明理由．