kt chuong i

<span class='text_page_counter'>(1)</span>TRƯỜNG THCS VÕ THỊ SÁU TỔ: TOÁN – TIN –LÝ – CN. ĐỀ KIỂM TRA CHƯƠNG I MÔN: ĐẠI SỐ 8 ( Thời gian: 45 phút không kể thời gian giao đề) Điểm. Lời phê của giáo viên. Họ và tên:…………………………. Lớp:……….. Bài 1:( 2 điểm) Thực hiện phép tính a) 7x(2x-5)+(4x – 3)(x + 2) – 16x2 b) (x + y)( x2 – xy + y2) +(x – y)( x2 +xy +y2) Bài 2: (3,0 điểm) Phân tích các đa thức sau thành nhân tử: a) 5x2y + 10xy2 ; b) x3 + 2x2 + x c) xy + y2 – x – y Bài 3: (2 điểm) Tìm x, biết: a) 3x3- 12x = 0 b) x2 – 5x – 6 = 0 Bài 4: (1,5 điểm ) Tính giá trị của đa thức: x2 – 2xy – 9z2 + y2 tại x = 6 ; y = - 4 ; z = 30. Bài 5: (1,5 điểm ) a) Tìm a để đa thức x3 + x2 – x + a chia hết cho x + 2. b) cho a2 + b2 + c2 = ab + bc + ca. Chứng ming rằng a = b = c BÀI LÀM ............................................................................................................................................................................ ............................................................................................................................................................................ ............................................................................................................................................................................ ............................................................................................................................................................................ ............................................................................................................................................................................ ............................................................................................................................................................................ ............................................................................................................................................................................ ........................................................................................................................................................................... ............................................................................................................................................................................ ........................................................................................................................................................................... ............................................................................................................................................................................ ........................................................................................................................................................................... ............................................................................................................................................................................ ........................................................................................................................................................................... ............................................................................................................................................................................ ........................................................................................................................................................................... ............................................................................................................................................................................ ............................................................................................................................................................................

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<span class='text_page_counter'>(3)</span> Đáp án và biểu điểm Bài Ý 1 1a. Nội Dung 2. x – 30x - 6. 1b. 2x3. 2.a 2.b. 5x2y + 10xy2 = 5xy(x + y) x3 + 2x2 + x = x(x2 + 2x + 1) = x(x + 1)2 xy + y2 – x – y. 2. 2.c. = y(x + y) – (x + y) = (x + y)(y – 1) 3 3.a. 3.b. 3x3 – 12x = 3x(x2 – 4) = 0  3x(x – 2)(x + 2) = 0  3x 0  x 0   x  2 0   x 2  x  2 0  x  2 x2 –5 x – 6 = 0  x2 – 6x + x - 6  x(x – 6) + (x - 6) = 0  (x – 6)(x + 1) = 0  x=6 x=-1. 4. Điểm 1,0đ 1,0đ 3đ 1,0 đ 0.5đ 0.5đ 0.5đ 0.5đ 2đ 0.25đ 0.5đ 0.25đ 0.25đ 0.25đ 0.25đ 0.25đ 2đ. x2 – 2xy – 9z2 + y2 = (x2 – 2xy + y2) – 9z2 = (x – y)2 – (3z)2 = (x – y – 3z)(x – y + 3z). 0.5đ 0.5đ 0.5đ. Thay x = 6 ; y = - 4 ; z = 30 vào biểu thức trên ta được: (6 + 4 -3.30)(6 + 4 + 3.30) = - 80.100 = - 8000 5. 0.5đ 1.5đ. 5a. 3. 2. x +x –x+a x+2 x3 + 2x2 x2 - x + 1 - x2 - x + a - x2 - 2x x+ a x+2 a-2 Để x3 + x2 – x + a  x + 2 thì a – 2 = 0  a = 2. 5b. a2 + b2 + c2 = ab + bc + ca. 0.5đ 0.25đ.

<span class='text_page_counter'>(4)</span> ⇔. a2 + b2 + c2 - ab - bc – ca = 0. ⇔ 2a2 +2 b2 + 2c2 -2 ab - 2bc – 2ca = 0 ⇔ (a2- 2ab + b2)+( b2 – 2bc + c2)+(c2 – 2ac +a2) = 0 ⇔ (a – b )2 +( b – c)2 + ( c – a)2 = 0 ⇔ a – b = 0, b – c = 0, c – a = 0 ⇔ a= b = c. 0,25đ 0.25đ 0.25đ.

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