Đáp án:
a) ( 3x + 1 )^2 - 4(x - 2 )^2
= (3x)^2 + 2.3x.1 + 1^2 - 4 ( x^2 - 2.x.2 + 2^2 )
= 9x^2 + 6x + 1 - 4x^2 + 16x - 16
= 5x^2 + 32 - 15
b) 9( 2x + 3 )^2 - 4( x + 1 )
= 9 [ (2x)^2 + 2.2x.3 + 3^2 ] - 4x -4
= 36x^2 + 108x + 9 - 4x - 4
= 36x^2 + 104x + 5
c) 125x^3 + 1
= ( 5x )^3 + 1
= ( 5x + 1 ) ( 25x^2 - 5x + 1 )
d) 8x^3 - 27
= ( 2x )^3 - 3^3
= ( 2x - 3 )^3 + 3.2x.3 ( 2x - 3 )
e) x^3+ 6x^2+ 12x+ 8
= x^3 + 3.x^2 . 2 + 3.x. 2^2 + 2^3
= ( x + 2 )^3
f) 1- 9x+27x^2-27x^3
= - ( 27x^3 - 27x^2 + 9x -1 )
= - [ (3x)^3 - 3.(3x)^2.1 + 3.3x. 1^2 + 1^3 ]
= - ( 3x - 1 )^3
Xin ctlhn ạ :333
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