いas
Osin(180°-0)=siné
194. S=△0AB+△OBC+△OCD+△ODA 8)a
=OA-OB-sin0+→OB-OC·sin(180°-0),
2
+小:OC-OD·sin0+
2
OD-OA·sin(180°-0)
2
-.OA·OB·sin0+-
1
OB-OC-sin0
2
-OC·OD·sin0+
2
1
-OD·OA·sin0
2
=(OA+OC)-0Bsin0+
(OA+OC)·ODsin0
=;(OA+OC)(OB+OD)sin0
三
2
00%3D0
2
1
-absin0
300+