11.3.1八年级数学下--角平分线的性质1(kuhoo专用).ppt

角平分线的性质(1) Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. 学****目标: 学****目标: 1. 通过操作、验证等方式, 掌握角平分线的性质定理 2. 能运用角的平分线性质定理解决简单的几何问题. Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. 复****提问 1、角平分线的概念一条射线一条射线把一个角把一个角分成两个相等的角, 分成两个相等的角, 这条射线叫做这个角的平分线。这条射线叫做这个角的平分线。 o B C A12 Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. P到直线 l的距离的是线段 PC 的长 Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. 如图,是一个平分角的仪器,其中 AB=AD,BC=DC. 将点 A放在角的顶点,AB 和 AD 沿着角的两边放下,沿 AC 画一条射线 AE,AE ?经过上面的探索,你能得到作已知角的平分线的方法吗?小组内互相交流一下吧! 探究 1--- 想一想 Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. A AB B M M N N C C 作法:⑴以O为圆心,任意长为半径作弧,交 OA 于 M, 交 OB 于 N. ⑵分别以 M,N 为圆心,大于的长为半径作弧,两弧在∠ AOB 的内部交于点 C. ⑶作射线 OC, 射线 OC 即为所求. 12 MN0 温馨提示:作角平分线是最基本的尺规作图,大家一定要掌握噢! 试一试由上面的探究可以得出作已知角的平分线的方法已知:∠ AOB. 求作:∠ AOB 的平分线. Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. 1〉平分平