Kt chuong i

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:
3x3- 12x = 0
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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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


2đ


3.a
 3x3 – 12x = 3x(x2 – 4) = 0

3x(x – 2)(x + 2) = 0



0.25đ

0.5đ
0.25đ


3.b
x2 –5 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

0.5đ
0.5đ

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

0.25đ


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