如图16,在平面直角坐标系中,直线与轴交于点,与轴交于点,抛物线经过三点.
(1)求过三点抛物线的解析式并求出顶点的坐标;
(2)在抛物线上是否存在点,使为直角三角形,若存在,直接写出点坐标;若不存在,请说明理由;
(3)试探究在直线上是否存在一点,使得的周长最小,若存在,求出点的坐标;若不存在,请说明理由.
解:(1)直线与轴交于点,与轴交于点.
,························································································· 1分
点都在抛物线上,
抛物线的解析式为························································ 3分
顶点······························································································· 4分
(2)存在··············································································································· 5分
············································································································· 7分
············································································································ 9分
(3)存在·············································································································· 10分
理由:
解法一:
延长到点,使,连接交直线于点,则点就是所求的点.
····················································································· 11分
过点作于点.
点在抛物线上,
在中,,
,,
在中,,
,,··············································· 12分
设直线的解析式为
解得
································································································ 13分
解得
在直线上存在点,使得的周长最小,此时.··· 14分
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