25.解:(1)如图所示:······························································································· 4分
(注:正确画出1个图得2分,无作图痕迹或痕迹不正确不得分) (2)若三角形为锐角三角形,则其最小覆盖圆为其外接圆;········································ 6分 若三角形为直角或钝角三角形,则其最小覆盖圆是以三角形最长边(直角或钝角所对的边)为直径的圆.····································································································································· 8分 (3)此中转站应建在 的外接圆圆心处(线段 的垂直平分线与线段 的垂直平分线的交点处).············································································· 10分 理由如下: 由 , , , 故 是锐角三角形, 所以其最小覆盖圆为 的外接圆, 设此外接圆为⊙ ,直线 与⊙ 交于点 , 则 . 故点 在⊙ 内,从而⊙ 也是四边形 的最小覆盖圆. 所以中转站建在 的外接圆圆心处,能够符合题中要求. ························································································ 12分 |