KÍNH CHÀO QUÝ THẦY GIÁO ,CÔ GIÁO GIÁO ÁN ĐIỆN TỬ NguyÔn thÕ vËn Thcs Lª QuÝ ®«n – BØm S¬n Nh÷ng h»ng ®¼ng thóc ®¸ng Nh÷ng h»ng ®¼ng thóc ®¸ng nhí nhí HS1 : Tính ( x + y )(x + y ) HS1 : Tính ( x + y )(x + y ) HS2 : Tính ( x – y )(x – y) HS2 : Tính ( x – y )(x – y) HS3 : Tính ( x – y )(x + y) HS3 : Tính ( x – y )(x + y) ( x + y )( x + y ) ( x + y )( x + y ) = x = x 2 2 + xy + xy + y + xy + xy + y 2 2 = x = x 2 2 + 2xy + y + 2xy + y 2 2 ( x – y )( x – y) ( x – y )( x – y) = x = x 2 2 – xy – xy + y – xy – xy + y 2 2 = x = x 2 2 – 2xy + y – 2xy + y 2 2 ( x – y )( x + y) ( x – y )( x + y) = x = x 2 2 + xy – xy – y + xy – xy – y 2 2 = x = x 2 2 – y – y 2 2 KiÓm tra bµi cò KiÓm tra bµi cò Bµi mét: Nh÷ng h»ng ®¼ng thøc ®¸ng nhí Bµi mét: Nh÷ng h»ng ®¼ng thøc ®¸ng nhí 1. B×nh ph­¬ng mét tæng 1. B×nh ph­¬ng mét tæng ( x + y) ( x + y) 2 2 = x = x 2 2 + 2xy + y + 2xy + y 2 2 ¸p dông: ¸p dông: ( x + 1 ) ( x + 1 ) 2 2 = ? = ? ( x + 2y ) ( x + 2y ) 2 2 = ? = ? 2. B×nh ph­¬ng cña m«t hiÖu 2. B×nh ph­¬ng cña m«t hiÖu ( x – y) ( x – y) 2 2 = x = x 2 2 – 2xy + y – 2xy + y 2 2 ¸p dông : ¸p dông : ( 2x – y ) ( 2x – y ) 2 2 =? =? ( x + 1 ) ( x + 1 ) 2 2 = x = x 2 2 + 2.x.1 + 1 + 2.x.1 + 1 2 2 = x = x 2 2 + 2x + 1 + 2x + 1 ( x + 2y ) ( x + 2y ) 2 2 = x = x 2 2 + 2.x.(2y) + (2y) + 2.x.(2y) + (2y) 2 2 = x = x 2 2 + 4xy + 4y + 4xy + 4y 2 2 ( 2x – y ) ( 2x – y ) 2 2 =(2x) =(2x) 2 2 – 2.(2x).y + y – 2.(2x).y + y 2 2 =4x =4x 2 2 – 4xy + y – 4xy + y 2 2 C¸ch lµm nµo sau ®©y lµ ®óng : C¸ch lµm nµo sau ®©y lµ ®óng : C¸ch 1 C¸ch 1 ( 3x – 2 ) ( 3x – 2 ) 2 2 = 3x = 3x 2 2 – 2.3x.2 + 2 – 2.3x.2 + 2 2 2 = 3x = 3x 2 2 – 12x + 4 – 12x + 4 C¸ch 2 C¸ch 2 ( 3x – 2 ) ( 3x – 2 ) 2 2 = (3x) = (3x) 2 2 – 2(3x)(2) + (2) – 2(3x)(2) + (2) 2 2 = 9x = 9x 2 2 – 12x + 4 – 12x + 4 SAI SAI §óng §óng 3.HiÖu cña 2 b×nh ph­¬ng : 3.HiÖu cña 2 b×nh ph­¬ng : x x 2 2 – y – y 2 2 = ( x – y )( x + y ) = ( x – y )( x + y ) ¸p dông: ¸p dông: x x 2 2 – (3y) – (3y) 2 2 = ? = ? 4x 4x 2 2 – y – y 2 2 = ? = ? x x 2 2 – (3y) – (3y) 2 2 = ( x – 3y )(x + 3y) = ( x – 3y )(x + 3y) x x 2 2 – y – y 2 2 = (2x) = (2x) 2 2 – y – y 2 2 = ( 2x – y )( 2x + y) = ( 2x – y )( 2x + y) BT1 :ViÕt thµnh b×nh ph­¬ng mét tæng: BT1 :ViÕt thµnh b×nh ph­¬ng mét tæng: x x 2 2 + 6x + 9 + 6x + 9 = x = x 2 2 + 2.x.3 + 3 + 2.x.3 + 3 2 2 = (x + 3) = (x + 3) 2 2 BT2: ViÕt thµnh binh ph­¬ng mét hiÖu : BT2: ViÕt thµnh binh ph­¬ng mét hiÖu : – – 10x + x 10x + x 2 2 + 25 + 25 = x = x 2 2 –10x + 25 –10x + 25 = x = x 2 2 –2.x.5 + 5 –2.x.5 + 5 2 2 = (x – 5) = (x – 5) 2 2 Ph¸t triÓn kh¶ n¨ng t­ duy Ph¸t triÓn kh¶ n¨ng t­ duy