[10分!!功課]deductive geometry

圖片參考：http://us.f2.yahoofs.com/hkblog/QytE0ImcBRoyn9FhLuLvSJJq4Q--/blog/ap_20070423071449831.jpg?ibAopLGBamklkYHd

Just teach you no.1 ... as ALL are easy indeed
1.
a + c = 180° (adj. ∠s on st line) ---(1)
b + d = 180° (adj. ∠s on st line) ---(2)
(1) - (2)
a - b + c - d = 0
a - d = b - c
Since b = c (given)
b - c = 0
SO a - d = 0 ---> a = d

HINTS :
2.
Use vert. opp. ∠s
3.
Use SAS
4.
Use SSS
5.
Use ASA