角平分线是指把一个角分成两个相等的角的射线.关于角平分线具有如下重要的性质:角平分线上的点到角的两边的距离相等.对于一些含角平分线条件的证明问题,巧用这个性质,能简化解题过程,达到事半功倍的效果例1如图,△ABC中,AD平分∠BAC交BC于D,且BD=CD,DE、DF分别垂直于AB、AC, The bisector of the angle is the ray that divides an angle into two equal angles. The bisector has the following important properties: the distance from the point on the angle bisector to the two sides of the angle is equal. Proof of some conditions with angle bisectors The problem, clever use of this property, can simplify the problem solving process and achieve a multiplier effect. Example 1 As shown in Figure 1, in ABC, AD divides BAC into BC in D, and BD=CD, and DE and DF are perpendicular to AB and AC, respectively.