1 2 1. 2. . AB CDE 10 CD 4m BD 6m. ABC . ABC A B C AD ABC A D A B C AD A D 1 2 A B C 20cm ABC . ABC A B C k AD A D 1 2 ABC A B C 1 2 . A B C 20cm ABC 20 1 2 . ABC 10cm. ABC A B C AD A D 1 2 ABC A B C A B C ABC . ABC BC AC D BC DC AC ACB CF AD F E AB EF. BDFE 6 ABD . CF ACB DC AC CF ACD F AD . E AB EF BD EF BD 1 2 . B AEF ADB AFE AEF ABD S AEF S ABD 1 2 2 1 4 . S AEF S ABD S BDFE S ABD 6 S ABD 6 S ABD 1 4 . S ABD 8 ABD 8. EF BD 1 2 S AEF S ABD 1 2 S AEF S BDFE 1 2 . . 2 . . .