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3'!!6!!4!8!!#Q!K716!!#Q a,T G!#!&!# ,?!#I  GV!=E!F&/6D&,<C!5G!|!w67#&-F!8!@I&C!d HS .',Q!~Q!&6&!=E&/6DR   !"#$"%&'(%)( * +, &/012,(3 M@%N, O:P:" sK!!"#%Z3B[] W2'/,<7<'\','/,< SVlmlnoB S_mpqpW_rstB Trang 4 s'1$)*<2%] B!%Z3B[&, „ A yAH  & „ B y•  & „ C y•H   x1!*[] x0 *[] B<'EC',Q 117 75 65 B D C A „ D y@A  AH  •  •H  y@  S*[,?••  4  2,.5, 60&#7"8(908,:;<,="<2%6(>,"% 7,?@"8 Hoạt động 1Hình thành định nghĩa 7D,<C!5-!8!@#! 0Z3 B[*8 a,T] #.%'!8!!#_4!8! !#'!8!!=!] S_/' K!!u!8!!#/. ! 7D,<C!5-!8!H&!', 4C] M K N I G H E F A C D B c) b) a) 75 0 120 0 115 0 75 0 105 0 60 0 60 0  !4vb!!0' $ B!']G-F!8!A&•6I B!!4vbQ,< …,4C7/!u/6'4] O$"%"8%Q0G6I H B A C D caïnh beân caïnh beân caïnh ñaùy caïnh ñaùy 8!!#Z3B[GZ3zzB[I Z3&B[!  Z[&3B!,/ Z =\# ƒ#*6$2!,/+#!8!!# !8,P!# C D B A D B A C ƒ!4vbG67#•I Hoạt động 2 Hình thang vuông B!U#!8!&1! D „ ] *Z3B['!8!!#^_4! '!8!!#^] !# hinh thang comot gocvuong  ⇔   *R"%&%0"8<@S"8 A B D C R"%&%0"8<@S"8'hìnhthang*1 goc vuông A +, &/0#:"%8,: 1/Bài 7 trang 71 7D,<C!5!8!-G6I 1/Bài 7 trang 71 #Ivy  ~yY  ,Ivy•  ~yH   SVlmlnoB S_mpqpW_rstB Trang 5 A B C D A C B A B C D D c) b) a) y x 65 0 y x 70 0 50 0 y x 40 0 80 0  S.7<'\!X…7=\!>C z_15B CTE!!8!!#Z3B[GZ3zz B[I* µ µ Z [= 1!0 *Z[  S_!=E•!-!8!z!-!D  7!8!!#&*6$!,/*z 8] !'/<,< Ivy€  ~yH  z_15B CTE  D C B A #* µ µ  Z [ + = Gz!8! !#I W µ µ Z [= GI/  µ µ µ    [ [  [  @ A + = = = D F5"8?G"H"%2 .,!2 K!!"#!8!!#&!8!!#^ Bài tập 8 trang 71 Sgk J K+L  ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ A  @  4U  O!%! K!!"#&1!!dd!T!4,!8!!#| 345 K!!"#&1!!d!8!!#|7T!4!%! ,4C*'/U# O"†‡ˆ6"†C!|1!<!&6'4+#2 K!'1O"†78!,'\ <+#2, ! 2S51!{!4&!1!v7'4C'4!%!  GV!=E!#6!<&!=E *&C#~,<C!5 HS .,h&',Q!~55!=E!#6!<!=E *R  SVlmlnoB S_mpqpW_rstB Trang 6  !"#$"%&'(%)( * +, &/012,(3 M@%N, O:P:" sK!!"#!8!!#G/7`0 +#*IG I z3z• '!D/+#S_G I z3z•G I #* µ µ  Z [ + = Gz!8!!#I W µ µ  Z [ − = GI / µ Z yG  x  Iy  µ [ y  ‰  y  Wa6! µ µ  3 B + = Gz!8!!#I  µ µ 3 B= GI _4 µ µ  B B + =  µ   B  @ A⇒ = = µ   3 A = = 4  2,.5, 60&#7"8(908,:;<,="<2%6(>,"% 7,?@"8 Hoạt động 1Hình thành định nghĩa B*!4vb8$!8!!#7/G7 $ 67#I] W2!8!!#!=4.'!8!!# |_4!8!!#|'!8!!=!] S_*f6!,< s=#7#]7/,<C!5G!aC!7I H G F E A B C D 110 0 100 0 80 0 80 0 80 0 80 0 b) a) T S Q P N M K I 70 0 70 0 110 0 d) c) S_!0',?!!i7/!8!- 1.Định nghĩa: R"%&%0"8(M"'hình thang*2 góc kề 1 đáy bằng nhau A B C D 8!!#|Z3B[ Z3zzB[ Šy „ B ~ „ „ By[ SVlmlnoB S_mpqpW_rstB Trang 7 <!1!…7=\!>C ‹#,#!8!!#|7/&*!4vb !'8] Hoạt động 2 Tìm tính chất cạnh bên B! !,/+#,#!8!!# |Q!8!Y B*!:6'48] #!%! $ *] S_-!8!&!!S&OŒ 7=\!>C!,/Z[3B6!^ &6b!!e!#m ∆m[BmZ3'#8] !C!!.4C&!!4vbQ ,< 7=\!>CZ[zz3B] S_!!#*!#!,/!8 !#!,/,?!#=>'&!8!!# *!#!,/,?!#*C!<'!8! !#|6!^] 7D!8!•/!efG6 BG67#•@I 7D,<C!5G!8!@6I !D K!'1&!8!!#|Z3B[*!# !F,?!#] 2.Tính chất : a) Định lí 1: 7hình thang cân&!#cạnh bên bằng nhau O C D A B 2 2 1 1 S Z3B['!8!!#| OŒ Z[y3B b) Định lí 2: A B C D 7hình thang cân&!#đường chéo bằng nhau Hoạt động 3: Tìm dấu hiệu nhận biết hình thang cân S_!']@ Œ! :- => :Z&3!2 #!Z3B['!8!!#*!# =\ !bZBy3[]G>fPC#I B!!4vb!0' xB!-Z&3!uu 6 xq!,: K!'1@!,< [d!T!4,!!#|] S_!0'&!,< 4VW@%,X@"%Y"1,Z&%R"%&%0"8(M" #IĐịnh Lí 3: Sgk trang 74 ,I[d!T!4,!8!!#| 1. 8!  !#* !# góc kề một đáy bằng nhau ' hthang cân 2. 8!!# * hai đường chéo bằng nhau 'hthang can A +, &/0#:"%8,: SVlmlnoB S_mpqpW_rstB Trang 8 _15B CTEB!!8!!#|Z3B[ GZ3zzB[~Z3•B[IOc =\# Z&3O+#!8!!#B!%!7? [yBO S_ . $z!!bC $ S_!=E•!-!8!z!-!D Ž*!4vb8$!##^] !'/<,<  K H D C B A # ∆  Z[ ∆  O3B* Z[y3BGz!8!!#|I µ µ [ B= Gz!8!!#|I / ∆  Z[y ∆  O3BG!&I 7#Zy3BG CI D F5"8?G"H"%2 .,!2 K!!"#&1!!d&d!T!4, - Bài tập 12,15,17,18 trang 74,75 Sgk J K+L  ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ A  Y [L\  ƒO!% .! =>+0!!T'f! K!!"#&1!!d!8!!# |&d!T!4,2!8!!#| .!,451!!d+#!8!!#| :<20,4C) !>C ƒO"†‡ˆ6"†!#&C!|1!)!>C :<U,4C ƒ! 2S50'/!T,T!%+#948!!#|E# |&!#*Q +#!8!!#|E =\!b  GV3<C!5! $6:7#&,4C HS.,',4C u! u =>!=E•   !"#$"%&'(%)( * +, &/012,(3 M@%N, O:P:" Œ,Hz•H6 S< #I#*#Z3B|Z SVlmlnoB S_mpqpW_rstB Trang 9 50 B C A D E B!!4vbQ,< s!~6!F K!!!X' e~ }#'!!X#+#/ !'!z%'!8!!# | y•  „  „ „  A CB − == Z[yZŽy•#Z[Ž|Z y•  „  „„  A DEAEDA − ==  „  „„  A EDAB − == W EDAB „ ~ „ '!#*QK71 (K ⇒[Žzz3B 8!!#3[ŽB*  „ „ B C=  /'!8! !#|G I 4  2,.5, 60&#7"8(908,:;<,="<2%6(>,"% 7,?@"8 Hoạt động 1Luyện tập 1/ Bài 12 trang 74 Sgk -!8!<,<E!<=; 9157=E 2/ Bài 17 trang 75 Sgk B! . $,&S_-!8!'/,<& .*6' S !!#Z3B[GZ3zzB[ „ „ ZB[y3[B I OŒ Z3B[| B!%!Z3B['!8!!#|!= !] _E $6T „ „ ZB[y3[B &#*!:!% ! =>8]y• B!%!!/8#] y•] … *y•] 1/ Bài 12 trang 74 Sgk F E D C B A # ∆  ŽZ[ ∆  •3B* Z[y3BGz!8!!#|I µ µ [ B= Gz!8!!#|I / ∆  ŽZ[y ∆  •3BG!&I 7#[ŽyB•G CI 2/ Bài 17 trang 75 Sgk  O BT 17/ 75 A B C D S.m'# :+#ZB3[&#* #*Z3zzB[GI / „ „ mZ3ymB[ G^'D7I  „ „ m3Zym[B G'D7I [ *∆mZ3|m SVlmlnoB S_mpqpW_rstB Trang 10 S.<~6!'!C B!!4vbQ,< S_!!i!,! GV: s:z! K!'1@!8P8!: , Bài 18 trang 75 Sgk ‘z! . $&6', s:#3[Ž|!8# $8] Œ!! 3[y3Ž] ‘z!'/,<78!, …|#y• $8] O! *!##ZB[#3[B ,?!#!Dz!] S.D'/,<'|, ##ZB[3[B,?!#7# => /’8] _4!8!!#Z3B[**B,?* '!8!!#8] ⇒mZym3GI Œ* „ „ m[BymB[ GI  mBym[GI …GIGI⇒ZBy3[ Bài 18 trang 75 Sgk BT 18/ 75 E D C B A GI>I a/ AB zzBŽy•%Z3ŽB'!8! !# WZBzz3Ž~ZBy3ŽGvI [ZBy3[GI~3[y3Ž O! *#3ŽB|3 ,z…|#zy• ¼ ¼ BED BDE= Wa6!* ¼ ¼ BEC ACD= ( đv) => ¼ ¼ ACD BDC= Khi *vb#  “ACD BDCV V B*ZBy3[  ¼ ¼ ACD BDC= [B! y• ACD BDC = V V GI z…y• C D= ) ) /!8!!#Z3B['!8!!# |G!,I A +, &/0#:"%8,: S.!'6!% u!.7”&”@ B!0'!!%!!8!!#| D F5"8?G"H"%2 J''f!vD',4C u' - 3_Az•Hz6 J K+L  ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ € SVlmlnoB S_mpqpW_rstB [...]... li v phỏt biu nh lớ D K C ng thng HK l trc i xng ca GIAO AN HINH HOC 8 GV SOAN: PHAM VN C Trang 26 hỡnh thang cõn ABCD 4/ Kim tra ỏnh giỏ: - Bi 35 trang 87 Sgk - Bi 35 trang 87 Sgk ! Treo bng ph v gi HS d lờn v - Bi 37 trang 87 Sgk ! Cho HS xem hỡnh 59 sgk v hi : Tỡm cỏc hỡnh cú trc i xng - Bi 37 trang 87 Sgk 5/ Hng dn nh: Bi 36, 38 trang 87 Sgk IV- RT KINH NGHIM : ***********************... DAB) 1 2 b) EF= (AB+CD)= 1 (6+10)=8cm 2 1 AB = 3cm 2 1 KF = AB = 3cm 2 EI = IK=EF(EI+KF)= 8( 3+3)=2cm 5/ Hng dn nh: - ễn tp li phn lý thuyt v xem li cỏc bi tp ó lm nm c cỏch lm - BTVN: 27/ 80 /sgk IV- RT KINH NGHIM : *********************** PHN XET DUYấT GIAO AN HINH HOC 8 GV SOAN: PHAM VN C Trang 18 Ngy son: 6.9.2011 Ngy dy : Tun : 4 Tit : 8 Đ5 DNG HèNH BNG THC V COMPA ... 20 trang 79 Sgk GIAO AN HINH HOC 8 DE= 50 cm T DE = ẵ BC (nh lý 2) => BC = 2DE=2.50=100 GV SOAN: PHAM VN C Trang 13 A x I 8 cm 500 K 8cm 5 00 1 0cm B C Bi 20 trang 79 Sgk à ã Ta cú C = AKI = 500 ( ng v,gt ) IK // BC M KA = KC = 8 (cm) Nờn AI = IB (l 1) Hay x = 10cm 5/ Hng dn nh: - Thuc nh ngha, nh lớ 1, 2 Xem li cỏch cm nh lớ 1,2 Sgk - Bi tp 21 trang 79 Sgk - Bi tp 28 trang 80 Sgk IV- RT KINH NGHIM... thc t thỡ ụi khi ta cng phi chn ng i phự hp tit kim c thi GIAO AN HINH HOC 8 Vy ) ) ẳ + ẳ = 2(O + O ) AOB AOC 1 3 => BOC = 2 xOy = 2.500 = 1000 Bi 39 trang 88 Sgk B A E d D C C i xng vi A qua d, D d nờn AD = CD AD+DB=CD+DB = CB(1) Tng t i vi im E ta cú GV SOAN: PHAM VN C Trang 28 gian nhng khụng c vi phm lut giao thụng Bi 40 trang 88 Sgk - GV treo bng ph ghi hỡnh 61 Quan sát mô tả bin báo giao thông... AB // CD ta cú iu gỡ ? + Cú AC = BD = 4cm ta suy ra iu gỡ ? + Kt lun ? Bi 34 trang 83 Sgk - Chia nhúm hot ng Thi gian lm bi l 5 cho cỏch dng v 2 cho chng minh - Nhc nh HS khụng tp trung lm bi GIAO AN HINH HOC 8 Ni dung Bi 33 trang 83 Sgk y B A z 4 D 80 3 C x Cỏch dng: + Dng on CD = 3cm + Qua D dng Dx to vi Dy 1 gúc 80 0 + Dng cung tron tõm C bỏn kớnh 4cm.Cung ny ct Dx ti A + Qua A dng tia Az // DC +... thng hng x K Q 3/ Bi tp 26 trang 80 Sgk - GV v hỡnh 45 v ghi bi tp 26 lờn bng - Gi HS nờu cỏch lm Ni dung Bi tp 25 - Cho c lp nhn xột bi gii bng GIAO AN HINH HOC 8 F K E D C Gii EK l ong trung bỡnh ca ABD nờn EK //AB (1) Tng t KF // CD (2) M AB // CD (3) T (1)(2)(3)=>EK//CD,KF//CD Do ú E,K,F thng hng Bi tp 26 trang 80 Sgk A C E - Cho c lp lm ti ch, mt em lm bng B A G 8cm B x D F 16cm y H Ta cú: CD... ca hỡnh thang ABFE Do ú: CE = (AB+EF):2 hay x = (8+ 16):2 = 12cm - EF l ng trung bỡnh ca hỡnh thang GV SOAN: PHAM VN C Trang 17 CDHG Do ú : EF = (CD+GH):2 Hay 16 = (12+y):2 => y = 2.16 12 = 20 (cm) 4/ Kim tra ỏnh giỏ: - Nờu bi tp 28 - V hỡnh, túm tt GT KL? - Lu ý HS cỏc kớ hiu trờn hỡnh v ! Gi ý cho HS phõn tớch: a) EF l tb ca hthang ABCD Bi tp 28 trang 80 Sgk B A E I K F D EF//DC C EF//AB AE=ED EK//DC... M O l gỡ ca HK ? Bi 48 trang 93 Sgk - Do ú O l gỡ ca AC ? B - Cho HS lờn bng trỡnh by E A - Gi HS nhn xột Bi 48 trang 93 Sgk F - Cho HS c V hỡnh nờu GT-KL H - Cho HS chia nhúm hot ng Thi gian lm bi 5 D G C ! Ni BD v AC Da vo du hiu hai cp cnh i song song S dng ng trung T giỏc ABCD bỡnh ca tam giỏc EB=EA ; FB=FC - Gi i din nhúm lờn trỡnh by - Cỏc nhúm nhn xột GIAO AN HINH HOC 8 GT GC=GH ; HA=HD KL... cho HS II CHUN B CA GV V HS: - GV : Compa, thc thng, thc o gúc, kim tra 15p GIAO AN HINH HOC 8 GV SOAN: PHAM VN C Trang 27 - HS : Compa, thc thng, thc o gúc, ụn tp kim tra 15p III TIN TRèNH LấN LP: 1/ n nh t chc: 2/ Kim tra: khụng 3/ Bi mi : Hat ng ca giỏo viờn v hc sinh Hot ng 1 : Luyn tp - Y/c hs c ni dung bi 36/ 87 , sau ú v hỡnh - AOB l tam giỏc gỡ ? Vỡ sao ? - M Ox l ng trung trc ca AB nờn ta cú... ca AB nờn ta cú iu gỡ ? Suy ra ? - Tng t ẳ bng gỡ ? AOC => AOB + AOC =?, O1 + O3 =? Ni dung Bi 36 trang 87 Sgk C y A 500 x O - Gi HS lờn bng trỡnh by - Cho HS nhn xột B Ta cú AOB l tam giỏc cõn vỡ OB=OA Nờn Ox l tia phõn giỏc ca AOB AOB Suy ra ẳ = 2O1 AOC Tng t : ẳ = 2O3 Bi 39 trang 88 Sgk - Y/c hs c bi 39 - Gi HS v hỡnh, vit GT- KL a) C i xng vi A qua d, D d nờn ta cú iu gỡ ? - AD+DB= ? - . 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