Kiểm tra môn đại số 8 thời gian: 45 phút Trường THCS Thượng Lan
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Trường THCS Thượng Lan Lôùp : 8…… Hoï & Teân :…………………………………………… KIEÅM TRA M ÔN ÑAÏI SOÁ 8 Thời gian: 45 phút Thø …… ngµy……. th¸ng ……. N¨m 2008 Điểm Lời phê của thầy , cô giáo BAØI LAØM ÑEÀ SOÁ 1 I/ TRAÉC NGHIEÄM : (3 ñieåm). 1) Gheùp moãi doøng ôû coät traùi vôùi keát quaû ôû coät phaûi ñeå ñöôïc moät keát quaû ñuùng: a) x – y 1) (x - y ) .( x + xy + y) b) (x – 2 ) 2) (x – y ).( x + y) c) x – y 3) x + 9x + 27x + 27 d) (x + 3 ) 4) (x – 2 ). ( x + 2x + 4) 5) x – 4x + 4 2) Khoanh troøn chöõ caùi ñöùng tröôùc caâu traû lôøi ñuùng : a) Ña thöùc 2x – 1 – x ñöôïc phaân tích thaønh : A/ (x – 1 ) B/ – (x + 1 ) C/– (x – 1 ) D/ (– x – 1 ) b) Ruùt goïn bieåu thöùc x.(x – y ) + y.(x – y ) ñöôïc : A/ x + y B/ x– y C/ y– x B/ – y– x c) Keát quaû cuûa pheùp chia ña thöùc : 2xy +6xy – 4xy cho ña thöùc 2xy laø : A/ 2x – 4xy + 1 B/ x – xy + 5 C/ x +3xy – 2y D/ Moät keát quaû khaùc d) KÕt qu¶ ph©n tÝch ®a thøc 3x - 12x thµnh nh©n tö lµ A. 3x( x- 4) B. 3x(x – 2) C. 3x( x + 2) (x – 2) D. 3( 3x – 2) ( 3x + 2) II/ TÖÏ LUAÄN: (7 ñieåm). Baøi 1: (1,5ñieåm) Thöïc hieän pheùp tính: a, 4x (5x2 - 2x -1) …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… a , ( x +3y ) (x2 – 2xy +y ) ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… Baøi 2 : (2ñieåm) Phaân tích ña thöùc thaønh nhaân töû : a) x– y–2x + 2y …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b) x– 6x + 5 ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… Baøi 3 : (2ñieåm) Thöïc hieän pheùp chia a) (3x2y2 + 6x2y3 - 12xy) : 3xy ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… b) (x3-3x2+5x -6): (x2 – x + 3 ) ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… Baøi 4 : (1ñieåm) Vôùi giaù trò naøo cuûa m ñeå ña thöùc : x4 - 2x3 + 3x2 - 4x + m chia heát cho ña thöùc: x+2 …………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… Baøi 5 : (0,5ñieåm)Chöùng minh raèng : x – 12x + 50 > 0 vôùi moïi x Î R …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Thø …… ngµy……. th¸ng ……. N¨m 2008 KIEÅM TRA MÔN ÑAÏI SOÁ 8 Thời gian: 45 phút Trường THCS Thượng Lan Lôùp : 8…… Hoï & Teân :…………………………………………… Điểm Lời phê của thầy , cô giáo BAØI LAØM ÑEÀ SOÁ 2 I/ TRAÉC NGHIEÄM : (3 ñieåm). Caâu 1 : Gheùp moãi doøng ôû coät traùi vôùi keát quaû ôû coät phaûi ñeå ñöôïc moät keát quaû ñuùng: a) (x – y ) .( x + xy + y) 1) x + 2xy + y b) (x +y ) 2) x + 3x y + 3xy + y c) (x – y ).( x + y) 3) x+ y d) (x + y ) 4) x – y 5) x – y Caâu 2: Khoanh troøn chöõ caùi tröôùc caâu traû lôøi ñuùng : 1) x.( 2x ) baèng: A/ 3x – 1 B/ 3x- x C/ 3x+ x D/ x– x 2) x – x = 0 coù : A/ x = 0 B/ x =1 C/ x = 0 ; x = 1 D/ x = 0 ; x = – 1 3) 10xyzchia heát cho ña thöùc : A/ 7xyz B/ 5xyz C/ 2xyz D/ 10xyzt 4) (6x – 8x – 2x) : ( – 2x ) baèng : A/ 3x – 4x – 1 B/ – 3x – 4x – 1 C/ 3x – 4x +1 D/ – 3x + 4x +1 II/ TÖÏ LUAÄN: (7 ñieåm). Baøi 1 : (1,5ñieåm)Thöïc hieän pheùp tính: a) ( x2 -2xy +4 ).(2x y) …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b) (x2 + 3x + 2).(x+3) …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 2 : (2ñieåm)Phaân tích ña thöùc thaønh nhaân töû : a) b– c+ b + c …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b)( x+ 9) –36x …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 3 : (2ñieåm)Thöïc hieän pheùp chia a) (-18x3y5 + 12x2y2 - 6xy3) : 6xy …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b)(2x3 - 5x2 +9x – 14):(x - 2 ) …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 4 : (1ñieåm)Vôùi giaù trò naøo cuûa a ñeå ña thöùc : 6x- 7x– x + a chia heát cho ña thöùc : 2x + 1 …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 5 : (0,5ñieåm)Chöùng minh raèng : – x + 10x – 30 <0 vôùi moïi x Î R …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Thø …… ngµy……. th¸ng ……. N¨m 2008 Trường THCS Thượng Lan Lôùp : 8…… Hoï & Teân :…………………………………………… KIEÅM TRA MÔN ÑAÏI SOÁ 8 Thời gian: 45 phút Điểm Lời phê của thầy , cô giáo BAØI LAØM ÑEÀ SOÁ 3 I/ TRAÉC NGHIEÄM : (3 ñieåm). Baøi 1 : Gheùp moãi doøng ôû coät traùi vôùi keát quaû ôû coät phaûi ñeå ñöôïc moät keát quaû ñuùng: a) x + 1 1) x – 4 b) (x + 1 ) 2) x – 8 c) (x – 2 ).( x + 2) 3) x+ y d) x – 6x + 12x – 8 4) (x + 1)(x – x + 1) e) (x – 2 ). ( x + 2x + 4) 5) x + 4x + 4 f) (x + 2) 6) ( x – 2 ) 7) x + 3x +3x + 1 8) ( x – 4) Caâu 2: Khoanh troøn caâu ñuùng. a) Tính : (-4x)(5x-2y)=? A. –20x2-8xy B. 20x2 +8xy C. –20x2+8xy D. Caû a,b,c ñeàu sai. b) Kết quả của phép tính 15x2y2z : (3xyz) là A. 5xyz B. 5 x2y2z C. 15xy D. 5xy c) Kết quả của phép tính (2x2 - 32) : (x - 4) là A. 2(x – 4) B. 2 (x + 4) C. x + 4 D. x – 4 II/ TÖÏ LUAÄN: (7 ñieåm). Baøi 1 : (1,5ñieåm)Thöïc hieän pheùp tính: a) (5x2y – 3xy2+2x).4xy …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b) (2a – 1)(a2 – 5 +2a) …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 2 : (2ñieåm) Phaân tích ña thöùc thaønh nhaân töû : a) xy + xz –2y – 2z …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b) 25 – x+ 4xy – 4y …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 3 : (2ñieåm)Thöïc hieän pheùp chia (2x2y3 + 5x3y2 - 6x2y2):5xy2 …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b)(x4 + 2 x3 + 5x2 +10 x – 18) : (x – 1) …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi4 : Vôùi giaù trò naøo cuûa a ñeå ña thöùc : x+ x– x + a chia heát cho ña thöùc : x + 2 ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… Baøi 5 : (0,5ñieåm)Chöùng minh raèng :4 x + 4x+ 11 >0 vôùi moïi x Î R ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………… Điểm Lời phê của thầy , cô giáo Trường THCS Thượng Lan Lôùp : 8…… Hoï & Teân :…………………………………………… KIEÅM TRA MÔN ÑAÏI SOÁ 8 Thời gian: 45 phút Thø …… ngµy……. th¸ng ……. N¨m 2008 Điểm Lời phê của thầy , cô giáo BAØI LAØM ÑEÀ SOÁ 4 I/ TRAÉC NGHIEÄM : (3 ñieåm). Caâu 1: H·y ghÐp mçi biÓu thøc ë cét A víi mét biÓu thøc ë cét B ®Ó ®îc ®¼ng thøc ®óng A B 1, (x –y) (x+y ) a , x2 +2x +1 2, (x +1 ) 2 b, 9x2 +6x +1 3, (3x -1 )2 c, 9x2 -6x +1 4, (3x – 1 )3 d, x2 –y2 e , y2 –x2 f, 27x3 – 27x2+ 9x - 1 Caâu 2:Khoanh troøn chöõ caùi tröôùc caâu traû lôøi ñuùng : 1) Phaân tích ña thöùc x ( x – 2 ) + x – 2 thaønh nhaân töû : A/ (x – 2 ) . x B/ (x – 2 ).x C/ x (2x – 4 ) D/ (x – 2 ).( x+ 1) 2) Ñôn thöùc 8xyz chia heát cho ñôn thöùc naøo A/ 16xy B/ 2xyz C/ 0,3x y5 D/ xyz 3) Tích cuûa ñôn thöùc – 5x vaø ña thöùc 2x + 3x – 5 laø : A/ 10x–15x+25x B/ –10x–15x+25x C/ –10x–15x– 25x D/ Moät keát quaû khaùc 4) Giaù trò cuûa bieåu thöùc : ( - 5x y ) : 10x y taïi x = 100 , y = laø : A/ – 5 B/ C/ 5 D/ II/ TÖÏ LUAÄN: (7 ñieåm). Baøi 1 : (1,5ñieåm)Thöïc hieän pheùp tính: a) (3xy2z + 5xyz2+2xy).6xyz2 …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b) (2x – 3)(x2 + 6 – 2x) …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 2: (2ñieåm)Phaân tích ña thöùc thaønh nhaân töû : a) 3x+ 3xy – x – y …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b) 32 x – 18x …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 3 : (2ñieåm)Thöïc hieän pheùp chia a) (3xy4 – 2xy3 +10 xy2 ) :4xy2 …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… b) (x3 +3x2 – 4x - 12) : ( x2 + x – 6) ………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… Baøi 4: Vôùi giaù trò naøo cuûa a ñeå ña thöùc : 5x – 3x+ 7x– x + a chia heát cho ña thöùc : x – 2 ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ Baøi 5 : Chöùng minh raèng bieåu thöùc :A = x + 6 x + 11 > 0 vôùi moïi xÎ R ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ............................................................................................................................................................ ÑAÙP AÙN ÑEÀ SOÁ 1 I/ TRAÉC NGHIEÄM : (3 ñieåm). Caâu 1: gheùp ñuùng moãi yù cho 0,25ñ a -> 2 , b -> 5 , c -> 1 , d -> 3 Caâu 2: Moãi yù ñuùng cho 0,5 ñieåm a) C b) B c) C d) A II/ TÖÏ LUAÄN: (7 ñieåm). Baøi 1: (1,5ñieåm) Thöïc hieän pheùp tính: a, 4x (5x2 - 2x -1) = 4x.5x2 – 4x.2x -4x.1 0,25ñ = 20x3 – 8x2 -4x 0,2ñ a , ( x +3y ) (x2 – 2xy +y ) = x(x2 – 2xy +y ) + 3y(x2 – 2xy +y ) 0,25ñ =x3 – 2 x2y +xy + 3 x2y – 6xy2 +3y2 0,5ñ = x3 + x2 +xy – 6xy2 +3y2 0,25ñ Baøi 2 : (2ñieåm) Phaân tích ña thöùc thaønh nhaân töû : a) x– y–2x + 2y = (x– y) – (2x - 2y) 0,5ñ = (x + y)( x - y) – 2(x - y) 0,25ñ = (x - y) (x + y – 2) 0,25ñ x– 6x + 5 = x– x – 5x+ 5 0,25ñ = (x– x)- (5x- 5) 0,25ñ = x(x – 1) – 5(x – 1) 0,25ñ = ( x – 1)(x – 5) 0,25ñ Baøi 3 : (2ñieåm) Thöïc hieän pheùp chia a) (3x2y2 + 6x2y3 - 12xy) : 3xy = 0,25ñ = xy + 2x y2 – 4 0,25ñ b) (x3-3x2+5x -6): (x2 – x + 3 ) x3 - 3x2 + 5x - 6 x2 – x + 3 x3 – x2 + 3x x – 2 -2 x2 + 2x – 6 -2 x2 + 2x – 6 0 ( moãi böôùc ñuùng cho 0,5ñ) Baøi 4 : (1ñieåm) Vôùi giaù trò naøo cuûa m ñeå ña thöùc : x4 - 2x3 + 3x2 - 4x + m chia heát cho ña thöùc: x+2 x4 - 2x3 + 3x2 - 4x + m x+2 x4 + 2x3 x3- 4x2+11x – 26 - 4x3 + 3x2 - 4x + m - 4x3 – 8x2 11x2 - 4x + m 11x2+ 22x 0,5ñ - 26x + m - 26x - 52 m+ 52 Ñeå x4 - 2x3 + 3x2 - 4x + m chia heát cho ña thöùc: x+2 thì m+ 52 = 0 Þ m = - 52 0,5ñ Baøi 5 : (0,5ñieåm)Chöùng minh raèng : x – 12x + 50 > 0 vôùi moïi x Î R x – 12x + 50 = x – 2.x.6 + 36 +14 = x – 2.x.6 + 62 + 14 = (x – 6)2 +14 0,25ñ Vì (x – 6)2 ³ 0 vôùi moïi x Î R neân (x – 6)2 +14 ³ 14 > 0 vôùi moïi x Î R Hay x – 12x + 50 > 0 vôùi moïi x Î R 0,25ñ ÑAÙP AÙN ÑEÀ SOÁ 2 I/ TRAÉC NGHIEÄM : (3 ñieåm). Caâu 1: gheùp ñuùng moãi yù cho 0,25ñ a -> 5 , b -> 1 , c -> 4 , d -> 2 Caâu 2: Moãi yù ñuùng cho 0,5 ñieåm 1) B 2) C 3) A 4) D II/ TÖÏ LUAÄN: (7 ñieåm). Baøi 1 : (1,5ñieåm)Thöïc hieän pheùp tính: a) ( x2 -2xy +4 ).(2x y) = x2.2x y - 2x y. 2x y + 4. 2x y 0,25ñ = 2 x3 y – 2 x2 y2 + 8xy 0,25ñ b) (x2 + 3x + 2).(x+3) = x(x2 + 3x + 2) + 3(x2 + 3x + 2) 0,25ñ = x3 + 3x2 + 2x + 3x2 +9x +6 0,5ñ = x3 + 6x2 + 11x +6 0,25ñ Baøi 2 : (2ñieåm)Phaân tích ña thöùc thaønh nhaân töû : a) b– c+ b + c = ( b– c) + (b + c) 0,5ñ = (b + c) (b - c)+ (b + c) 0,25ñ = (b + c)(b – c + 1) 0,25ñ b)( x+ 9) –36x = ( x+ 9) - (6x) 0, 5ñ = (x+ 9 + 6x)( x+ 9 - 6x) 0,25ñ =( x+ 3) ( x- 3) 0,25ñ Baøi 3 : (2ñieåm)Thöïc hieän pheùp chia a) (-18x3y5 + 12x2y2 - 6xy3) : 6xy = -18x3y5: 6xy + 12x2y2:6xy - 6xy3 :6xy 0,5ñ = - 3 x2y4 + 2 xy - y2 0,5ñ b)(2x3 - 5x2 +9x – 14):(x - 2 ) 2x3 - 5x2 + 9x – 14 x - 2 2x3 - 4x2 2 x2 –x +7 - x2 + 9x – 14 - x2 + 2x 7x – 14 7x – 14 0 Vaäy (2x3 - 5x2 +9x – 14):(x - 2 ) = 2 x2 –x +7 (Moãi böôùc ñuùng vaø traû lôøi cho 0,25ñ) Baøi 4 : (1ñieåm)Vôùi giaù trò naøo cuûa a ñeå ña thöùc : 6x- 7x– x + a chia heát cho ña thöùc : 2x + 1 6x- 7x– x + a 2x + 1 6x- 7x 3 x2 – 5x +2 - 10x– x + a - 10x–5 x 0,5ñ 4x + a 4x + 2 a - 2 Ñeå 6x- 7x– x + a chia heát cho ña thöùc : 2x + 1 thì a – 2 = 0 Þ a = 2 0,5ñ Baøi 5 : (0,5ñieåm)Chöùng minh raèng :- x + 10x – 30 <0 vôùi moïi x Î R - x + 10x – 30 = -( x - 10x + 30) = - (x- 5)2 -5 0,25ñ Vì (x – 5)2 ³ 0 vôùi moïi x Î R Þ - (x – 5)2 £ 0 vôùi moïi x Î R neân - (x- 5)2 -5 £ - 5 <0 vôùi moïi x Î R Hay - x + 10x – 30 <0 vôùi moïi x Î R 0,25ñ ÑAÙP AÙN ÑEÀ SOÁ 3 I/ TRAÉC NGHIEÄM : (3 ñieåm). Caâu 1: gheùp ñuùng moãi yù cho 0,25ñ a -> 4 , b -> 7 , c -> 1 , d -> 6 , e -> 2 , f -> 5 Caâu 2: Moãi yù ñuùng cho 0,5 ñieåm: a) C b) D c) B II/ TÖÏ LUAÄN: (7 ñieåm). Baøi 1 : (1,5ñieåm)Thöïc hieän pheùp tính: a) (5x2y – 3xy2+2x).4xy = 5x2y .4xy – 3 xy2. 4xy + 2x.4xy 0,25ñ = 20x3y2 – 12x2y3 + 8x2y 0,25ñ b) (2a – 1)(a2 – 5 +2a) = 2a(a2 – 5 +2a) – 1(a2 – 5 +2a) 0,25ñ = 2a3 – 10a + 4a2 – a2 +5 – 2a 0,5ñ = 2a3 + 3a2 – 12a +5 0,25ñ Baøi 2 : (2ñieåm) Phaân tích ña thöùc thaønh nhaân töû : a) xy + xz –2y – 2z = ( xy+xz) – (2y-2z) 0,5ñ = x(y+z) – 2(y+z) 0,25ñ = (y + z)(x – 2) 0,25ñ b) 25 – x+ 4xy – 4y = 25 – (x- 4xy + 4y) 0,5ñ = 52 – ( x – 2y)2 0,25ñ = (5 + x – 2y)(5 – x + 2y) 0,25ñ Baøi 3 : (2ñieåm)Th
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