几何中的和差倍半问题
2011-06-02 12:29
225 查看
在四边形ABCD中,对角线AC平分∠DAB.
(1)如图①,当∠DAB=120°,∠B=∠D=90°时,求证:AB+AD=AC.
(2)如图②,当∠DAB=120°,∠B与∠D互补时,线段AB、AD、AC有怎样的数量关系?写出你的猜想,并给予证明.
(3)如图③,当∠DAB=90°,∠B与∠D互补时,线段AB、AD、AC有怎样的数量关系?写出你的猜想,并给予证明.
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912336287.png)
(1)如图1所示,在四边形
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912335141.png)
中,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912343613.png)
=
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912358498.png)
,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912377842.png)
与
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912389139.png)
相交于点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912395942.png)
,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912408874.png)
分别是
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912415777.png)
的中点,联结
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912428709.png)
,分别交
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912431642.png)
、
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912444574.png)
于点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912449525.png)
,试判断
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912456427.png)
的形状,并加以证明;
(2)如图2,在四边形
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912454966.png)
中,若
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912468280.png)
,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912471213.png)
分别是
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912471703.png)
的中点,联结FE并延长,分别与
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912485017.png)
的延长线交于点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912495475.png)
,请在图2中画图并观察,图中是否有相等的角,若有,请直接写出结论: ;
(3)如图3,在
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912494013.png)
中,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912507327.png)
,点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/20110606191251260.png)
在
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912523193.png)
上,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912528143.png)
,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912536615.png)
分别是
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912549930.png)
的中点,联结
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912554499.png)
并延长,与
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912569383.png)
的延长线交于点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912574267.png)
,若
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912577582.png)
,判断点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912586926.png)
与以AD为直径的圆的位置关系,并简要说明理由.
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061913009826.png)
两块等腰直角三角板△ABC和△DEC如图摆放,其中∠ACB =∠DCE = 90°,F是DE的中点,H是AE的中点,G是BD的中点.
(1)如图1,若点D、E分别在AC、BC的延长线上,通过观察和测量,猜想FH和FG的数量关系为_______和位置关系为_____ ;
(2)如图2,若将三角板△DEC绕着点C顺时针旋转至ACE在一条直线上时,其余条件均不变,则(1)中的猜想是否还成立,若成立,请证明,不成立请说明理由;
(2)如图3,将图1中的△DEC绕点C顺时针旋转一个锐角,得到图3,(1)中的猜想还成立吗?直接写出结论,不用证明.
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061913021198.png)
2003年黑龙江省
已知:如图,BD、CE分别是△ABC的外角平分线,过点A作AF⊥BD,AG⊥CE,垂足分别为F、G,连结FG,延长AF、AG与直线BC相交,易证:
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106101251288492.png)
,若:
(1)BD、CE分别是△ABC的内角平分线(如图2);
(2)BD为△ABC的内角平分线,CE为△ABC的外角平分线(如图3),则在图2、图3两种情况下,线段FG与△ABC三边又有怎样的数量关系?请写出你的猜测,并对其中的一种情况进行证明。
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106101251303150.png)
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106101251328016.png)
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106101251341594.png)
(1)如图①,当∠DAB=120°,∠B=∠D=90°时,求证:AB+AD=AC.
(2)如图②,当∠DAB=120°,∠B与∠D互补时,线段AB、AD、AC有怎样的数量关系?写出你的猜想,并给予证明.
(3)如图③,当∠DAB=90°,∠B与∠D互补时,线段AB、AD、AC有怎样的数量关系?写出你的猜想,并给予证明.
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912336287.png)
(1)如图1所示,在四边形
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912335141.png)
中,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912343613.png)
=
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912358498.png)
,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912377842.png)
与
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912389139.png)
相交于点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912395942.png)
,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912408874.png)
分别是
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912415777.png)
的中点,联结
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912428709.png)
,分别交
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912431642.png)
、
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912444574.png)
于点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912449525.png)
,试判断
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912456427.png)
的形状,并加以证明;
(2)如图2,在四边形
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912454966.png)
中,若
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912468280.png)
,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912471213.png)
分别是
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912471703.png)
的中点,联结FE并延长,分别与
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912485017.png)
的延长线交于点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912495475.png)
,请在图2中画图并观察,图中是否有相等的角,若有,请直接写出结论: ;
(3)如图3,在
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912494013.png)
中,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912507327.png)
,点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/20110606191251260.png)
在
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912523193.png)
上,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912528143.png)
,
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912536615.png)
分别是
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912549930.png)
的中点,联结
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912554499.png)
并延长,与
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912569383.png)
的延长线交于点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912574267.png)
,若
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912577582.png)
,判断点
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061912586926.png)
与以AD为直径的圆的位置关系,并简要说明理由.
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061913009826.png)
两块等腰直角三角板△ABC和△DEC如图摆放,其中∠ACB =∠DCE = 90°,F是DE的中点,H是AE的中点,G是BD的中点.
(1)如图1,若点D、E分别在AC、BC的延长线上,通过观察和测量,猜想FH和FG的数量关系为_______和位置关系为_____ ;
(2)如图2,若将三角板△DEC绕着点C顺时针旋转至ACE在一条直线上时,其余条件均不变,则(1)中的猜想是否还成立,若成立,请证明,不成立请说明理由;
(2)如图3,将图1中的△DEC绕点C顺时针旋转一个锐角,得到图3,(1)中的猜想还成立吗?直接写出结论,不用证明.
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106061913021198.png)
2003年黑龙江省
已知:如图,BD、CE分别是△ABC的外角平分线,过点A作AF⊥BD,AG⊥CE,垂足分别为F、G,连结FG,延长AF、AG与直线BC相交,易证:
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106101251288492.png)
,若:
(1)BD、CE分别是△ABC的内角平分线(如图2);
(2)BD为△ABC的内角平分线,CE为△ABC的外角平分线(如图3),则在图2、图3两种情况下,线段FG与△ABC三边又有怎样的数量关系?请写出你的猜测,并对其中的一种情况进行证明。
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106101251303150.png)
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106101251328016.png)
![](http://images.cnblogs.com/cnblogs_com/banianji/201106/201106101251341594.png)
相关文章推荐
- 暴力破解几何问题
- 计算几何中的精度问题(转)
- 计算几何与圆心和球有关的计算问题
- 计算几何---凸包问题
- 修水管问题 计算几何 投影
- 计算几何问题汇总--圆与矩形
- 一个几何问题和猜测
- 第三课,绘制几何图形的一些细节问题
- 几何问题。点线向量面积等模版。
- 外挂猖獗,玩家心寒;无能代理,违背承诺;精彩游戏,寿命几何?[冷静谈问题,提建议]
- sicily--1816. 平面几何问题
- 计算几何之大圆包含小圆问题
- ACM 计算几何中的精度问题
- 厦大C语言上机 1391 简单的几何问题
- 南阳 3 多边形重心问题(数学几何)
- poj1106-Transmitters 几何覆盖问题
- 车道检测问题探究(二)几何模型拟合
- 涨水问题 (简单几何+二分查找)
- [高频] 六.数学,几何计算,位运算常见问题
- 【漂浮法或线段树】 解决矩阵覆盖(计算几何)问题