如图所示,在Rt△ABC中,∠CAB=90°,AB=2,AC=
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.一曲线E过点C,动点P在曲线E上运动,且保持|PA|+|PB|的值不变,直线l经过A与曲线E交于M,N两点.
(1)建立适当的直角坐标系,求曲线E的方程;
(2)设直线l的斜率为k,若∠MBN为钝角,求k的取值范围.
考点分析:
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?请说明理由.
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