3. 1 1 _ _ _ 2 _ 3 A B C D 4 OA BOC P OA O P P OC P OB A B C D 5 ABC C=90 AB=13 AC=12 B 5 AC A B C D 6 O O O O A B C D 7 A 3 4 A 5 y= x A B C D 8 AB O AC AB 30 AC=CD 1 CD O 2 OA=2 AC 9 AB O AD DBC= A 1 BC O 2 OC AD OC BD E BD=6 CE=4 AD 10 AB O CD AB M B BE CD AC E BC 1 BE O 2 CD=6 tan BCD= 1 2 O 11 ABC O D OC sin= 1 2 D=30 1 AD O 2 AC=6 AD 12 A O OC A B OC=BC AC= 1 2 OB 1 AB O 2 ACD=45 OC=2 CD 13 P O PO O C O A AB PO E EAC= CAP PA O 14 A BC O AD BC D B O CA E G AD OG BE F AF CB P 1 BF=EF 2 PA O 3 FG=BF O 3 2 BD FG