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python/数学课程/【辅助圆问题】定线定长.md

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  • 因为C是定点,E是动点,CE长度固定,所以E一定在以C为圆心,以CE=2为半径的圆上!

  • 因为E在四边形内部,所以不是整个圆,而是一个\frac{1}{4}圆。

  • 数形结合解决问题:当E_0落在BC上时,\angle ABE最大, 最大值是90^{\circ}

  • BE_1CE_1垂直时,BE_1是圆的切线,此时\angle ABE最小

  • 根据三角函数知识知道E_1C=2, BC=4 \therefore \angle E_1BC=30^{\circ}

结论:60^{\circ}<=\angle ABE <=90^{\circ}