TRƯỜNG THCS VÕ THỊ SÁU        ĐỀ KIỂM TRA CHƯƠNG I

TỔ: TOÁN – TIN –LÝ – CN      MÔN: ĐẠI SỐ 8

                                                                       ( Thời gian: 45 phút không kể thời gian giao đề)

 

 

Họ và tên:………………………….

Lớp:………..

Điểm

Lời phê của giáo viên

 

 

 

 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)      x25x – 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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Đáp án và biểu điểm    

 

Bài

Ý

Nội Dung

Điểm

1

1a

1b

x2 – 30x - 6

2x3

1,0đ

  1,0đ

2

 

 

3đ

 

2.a

5x2y + 10xy2  = 5xy(x + y)

1,0 đ

2.b

      x3 + 2x2 + x    

   = x(x2 + 2x + 1)

   = x(x + 1)2

 

0.5đ

0.5đ

2.c

       xy + y2 – x – y

   = y(x + y) – (x + y)

   = (x + y)(y – 1)

 

0.5đ

 

0.5đ

3

 

 

 

3.a

3x3 – 12x = 3x(x2 – 4) = 0

    3x(x – 2)(x + 2) = 0

   

 

0.25đ

 

0.5đ

0.25đ

3.b

x25 x – 6 = 0

    x2 – 6x + x - 6

    x(x – 6) + (x -  6) = 0

    (x – 6)(x + 1) = 0

            x = 6

  x = - 1

 

0.25đ

0.25đ

0.25đ

0.25đ

4

 

 

2đ

 

 

       x2 – 2xy – 9z2 + y2 

   =  (x2 – 2xy + y2) – 9z2

   =  (x – y)2 – (3z)2

   =  (x – y – 3z)(x – y + 3z)

Thay  x = 6 ; y = - 4 ; z = 30 vào biểu thức trên ta được:

    (6 + 4 -3.30)(6 + 4 + 3.30) = - 80.100 = - 8000

 

0.

0.

 

0.5đ

 

0.5đ

5

 

 

1.5đ

           5a

           x3 + x2 – 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

 

 

 

 

 

 

0.5đ

 

0.2

 

5b

a2 + b2 + c2 = ab + bc + ca

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

 

0.2

 

 

0.2

 

 

nguon VI OLET