Question

Chọn câu sai.

A. ( x   –   1 ) 3   +   2 ( x   –   1 ) 2   =   ( x   –   1 ) 2 ( x   +   1 )

B. ( x   –   1 ) 3   +   2 ( x   –   1 )   =   ( x   –   1 ) [ ( x   –   1 ) 2   +   2 ]

C. ( x   –   1 ) 3   +   2 ( x   –   1 ) 2   =   ( x   –   1 ) [ ( x   –   1 ) 2   +   2 x   –   2 ]

 

D. ( x   –   1 ) 3   +   2 ( x   –   1 ) 2   =   ( x   –   1 ) ( x   +   3 )

Answer 1

Ta có

+ )   ( x   –   1 ) 3   +   2 ( x   –   1 ) 2     =   ( x   –   1 ) 2 ( x   –   1 )   +   2 ( x   –   1 ) 2       =   ( x   –   1 ) 2 ( x   –   1   +   2 )   =   ( x   –   1 ) 2 ( x   +   1 )

nên A đúng

+ )   ( x   –   1 ) 3   +   2 ( x   –   1 )     =   ( x   –   1 ) . ( x   –   1 ) 2   +   2 ( x   –   1 )     =   ( x   –   1 ) [ ( x   –   1 ) 2   +   2 ]  

nên B đúng

+ )   ( x   –   1 ) 3   +   2 ( x   –   1 ) 2       =   ( x   –   1 ) ( x   –   1 ) 2   +   2 ( x   –   1 ) ( x   –   1 )     =   ( x   –   1 ) [ ( x   –   1 ) 2   +   2 ( x   –   1 ) ]     =   ( x   –   1 ) [ ( x   –   1 ) 2   +   2 x   –   2 ]

nên C đúng

+ )   ( x   –   1 ) 3   +   2 ( x   –   1 ) 2       =   ( x   –   1 ) 2 ( x   +   1 )     ≠   ( x   –   1 ) ( x   +   3 )

nên D sai

Đáp án cần chọn là: D