1 . 甲、乙两位同学分别做下面这道题目:在平面直角坐标系中,动点
到
的距离比
到
轴的距离大
,求
的轨迹.甲同学的解法是:解:设
的坐标是
,则根据题意可知
,化简得
; ①当
时,方程可变为
;②这表示的是端点在原点、方向为
轴正方向的射线,且不包括原点; ③当
时,方程可变为
; ④这表示以
为焦点,以直线
为准线的抛物线;⑤所以
的轨迹为端点在原点、方向为
轴正方向的射线,且不包括原点和以
为焦点,以直线
为准线的抛物线. 乙同学的解法是:解:因为动点
到
的距离比
到
轴的距离大
. ①如图,过点
作
轴的垂线,垂足为
. 则
.设直线
与直线
的交点为
,则
; ②即动点
到直线
的距离比
到
轴的距离大
; ③所以动点
到
的距离与
到直线
的距离相等;④所以动点
的轨迹是以
为焦点,以直线
为准线的抛物线; ⑤甲、乙两位同学中解答错误的是________ (填“甲”或者“乙”),他的解答过程是从_____ 处开始出错的(请在横线上填写① 、②、③、④ 或⑤ ).
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