Đề kiểm tra số học 8 15 phút tháng 9 10

Trường THCS Thạnh Lợi
Lớp: 8A
Họ&Tên:………………
ĐIỂM
Bằng số

Bằng chữ

KIỂM TRA ĐỊNH KÌ
MÔN: TOÁN
THỜI GIAN: 15 PHÚT
(Không kể thời gian phát đề)
Chữ kí giám thị Chữ kí giám khảo
H&T:…………

Tuần: 17
Tiết PPCT: 13
Nhận xét của giám
khảo

H&T:…………

ĐỀ:
Bài 1. (4 điểm) Thực hiện phép tính:
b) ( x − 1) ( x + 1) − ( x + 2 )
Bài 2. (3 điểm) Phân tích các đa thức sau thành nhân tử:
a) 5x 2 − 5y 2
b) ( 5x − 3) ( x + 2 ) − 2x ( x + 2 )
Bài 3. (3 điểm) Tìm x, biết:
a) (3x + 1)(2x − 5)

a) ( x − 2 ) − x ( x + 1) = 5
2

2

b) ( x − 8)( x + 2 ) − ( x + 4 ) 2 = 0

BÀI LÀM:
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ĐÁP ÁN VÀ THANG ĐIỂM:
Bài 1:
a) (3x + 1)(2x − 5) = 6x2 – 13x – 5

2.0đ

b) ( x − 1) ( x + 1) − ( x + 2 ) = x2 – 1 – (x2 +4x + 4)
= – 4x – 5

1.0đ
1.0đ

2

Bài 2:
a) 5x 2 − 5y 2 = 5(x2 – y2)
= 5(x+y)(x – y)

b) ( 5x − 3) ( x + 2 ) − 2x ( x + 2 ) = (x+2)(5x – 3 – 2x)
= (x+2)(3x – 3)
= 3(x+2)(x – 1)

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Bài 3:
2
a) ( x − 2 ) − x ( x + 1) = 5
⇔ x 2 − 4x + 4 − x 2 − x = 5
⇔ −5 x = 1
1
⇔x=−
5
1
Vậy: x = −
5
b) ( x − 8)( x + 2 ) − ( x + 4 ) 2 = 0
⇔ x 2 + 2 x − 8 x − 16 − x 2 − 8 x − 16 = 0
⇔ −14 x − 32 = 0
32
16
⇔x=
=−
− 14
7
16
Vậy: x = −
7

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