1、2,两点确定一条直线
2、39.75,32,42
3、35
4、∠B和∠ACD
5、50
6、7,∠BAD、∠CAD、∠B、∠C、∠BAC、
∠ADB、∠ADC
7、M是线段AB、CD的中点,C、D分别是
线段AD、CB的中点
8、画图略
9、(1) ①∠POC = ∠POB;②∠EOC = ∠BOF等.
(2) ①“对顶角相等”,40;②BOC,20;(3)∠BOF = 90°- ∠BOC = 50°
10、(1)线段AC1、AC2、AB、C1C2、C1B、C2B; (2) 55;(3)
(n+1)(n-2)
11、∠AOB = ∠COD = 46°,∠AOD = 124°
12、(1)图略;(2)图略;(3)图略;
(4) AD = DB,BE = CE,∠BDE = ∠BAC,∠BED = ∠BCA,∠ABC = ∠ACB,
∠BED = ∠ABC;
(5) AE⊥BC;(6)如∠EAC与∠ECA互余,∠DEA与∠BED互余,如∠DEC与∠BCA互补,
∠EDA与∠DAC互补
13、∠BOD = ∠AOC,∠AOC = ∠COE,得∠BOD = ∠COE
14、由∠AOC与∠AOD互余,∠AOC与∠BOC互余,得∠AOD = ∠BOC.又∠AOE = ∠COE,所
以∠BOE = ∠DOE.所以OE是∠BOD的平分线