B/ (X + 3) (X2 – 3X + 9) – X (X – 1) (X + 1) – 27 = 0A/ 36X2 – 49 = 0 ( 6X)2 – 72 = 0 (0,25Đ)X3 – 3X2 + 9X + 3X2 – 9X + 27 – X (X2 – 1 ) – 27 = 0 (0,25Đ) (6X – 7 ) ( 6X + 7 ) = 0 (0,25Đ)X3 + 27 – X ( X2 – 1 ) – 27 = 0 (0,25Đ) X...

câu 10 : - BAI KIEM TRA DAI SO 8 CHUONG I 20102011
BAI KIEM TRA DAI SO 8 CHUONG I 20102011
Câu 10 : (2đ) Tìm x biết :b/ (x + 3) (x

2

– 3x + 9) – x (x – 1) (x + 1) – 27 = 0a/ 36x

2

– 49 = 0 ( 6x)

2

– 7

2

= 0 (0,25đ)x

3

– 3x

2

+ 9x + 3x

2

– 9x + 27 – x (x

2

– 1 ) – 27 = 0 (0,25đ) (6x – 7 ) ( 6x + 7 ) = 0 (0,25đ)x

3

+ 27 – x ( x

2

– 1 ) – 27 = 0 (0,25đ) x

3

– x

3

+ x = 0 (0,25đ)Ta có 6x – 7 = 0 7  (0,25đ) x = 0 (0,25đ)x 6Hoặc 6x + 7 = 0 7  (0,25đ)