平行線上的角及與三角形相關的角(2條數)

2010-11-28 8:10 am

4.http://s54.radikal.ru/i146/1011/93/bfee5ef544b8.jpg

圖中,DC及DB是角平分線,求x

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7.http://s009.radikal.ru/i310/1011/20/a24983e19e9d.jpg

圖中,AB=BC,AEFC、ADB和BGC是直線,求x和y。
(提示:利用等腰三角形的概念)

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第七條我陣係知第一個步驟係:

(5-2)x180度=540(內角和)

之後唔知..

唔該幫我計計呢兩條數
THX>.<

更新1:

第七題.. 點解y要除2?

回答 (1)

魔龍帝齊格益力多

2010-11-28 7:52 pm

✔ 最佳答案

DCB=a,DBC=b
_____________
2a+2b+80=180(< sum of tri)
2a+2b=100
a+b=50
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x+a+b=180(< sum of tri)
x=130degrees
______________________

2010-11-28 11:57:42 補充：
Add a line(HB) paraell to ED and FG:
HB is the bisector of y:

180-x+(y/2)=180(int.

2010-11-28 11:59:41 補充：
Add a line(HB) paraell to ED and FG:
HB is the bisector of y:

180-x+(y/2)=180(int. angle,HB//ED)
y=2x

x+80+(y/2)=180(int. angles,HB//FG)
2x+80=180
2x=100
x=50

y=100

2010-11-28 12:00:14 補充：
Your direction is wrong in Q7

2010-11-28 12:43:36 補充：
It is because HB is the angle bisector of y.

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