F.3 三角學證明題..急!!!!!!20分!!!!!!20分!!!!!!!!!

1. Draw a line passes through R and parallel to QP and ST
q = r1 (alt angles , //lines)
s = r2 (alt angles , //lines)
therefore angle QRS = q+s
2. x = p +2q+p (ext. angle of triangle)
=2p+2q
= 2(p+q)
=2(60)
=120
3. Let angle CAD= angle BAD=x
angle CPA=angleDAB=x (corr. angles, PC//AD)
angle PCA=angle CAD=x(alt. angles, PC//AD)
therefore, triangle PCA is an isosceles triangle.
since angle CPA=angle PCA
AC=AP (base angles equals)
4. Draw a line passes through C (the point of angle y) that is parallel to DE
Let F be a point that is at the left of C
angle DCF = z (alt angles, DE//CF)
angle BCF=z-y
since x+z-y=180
AB//CF (corr. angles equals)
hence AB//DE

solution請看圖...
1-2：
http://i105.photobucket.com/albums/m224/rainiechi/finish1_2.jpg
3-4：
http://i105.photobucket.com/albums/m224/rainiechi/finish3_4.jpg

2008-04-27 15:35:02 補充：
漏左少少野
第4題
x+a =180 之後應該加返1句：
∴MN//AB(int. ∠s, supp) [←我擺錯左，個reason應該寫係度]
然後先到∴AB//DE