2017秋九年级数学上册 4.3 相似多边形教案1 （新版）北师大版.doc

1 4.3 1. 2. 3. . 1 2 3 4 5 6 7 8 . 1 2 . 1 2 3 4 6 5 6 7 1 1 2 8 . 1 . 2 . 3 . ABCD EFGH EFGH ABCD . ABCD EFGH A E B F AB EF EF AB 6 8 3 4 EFGH ABCD 3 4 . . 2 ABCD AD BC EF BC EF ABCD AEFD EBCF. AD 3 BC 4 AE EB . AD EF EF BC EF AE EB . AEFD EBCF AD EF EF BC EF 2 AD BC 4 12 EF 12 2 3. AEFD EBCF AE EB AD EF 3 2 3 3 2. . AB 20m AD 30m ABCD . 1 A B C D ABCD 2 x y A B C D ABCD 1 2 x y . 1 A B C D ABCD . xm 30 2x 30 20 2x 20 x 0. 0 A B C D ABCD 2 x y 3 2 A B C D ABCD . A B C D ABCD 30 2x 30 20 2y 20 x y 3 2 . x y 3 2 A B C D ABCD . . .