3) ( 3x + 1 )² - 4 ( x - 2 )²
= 9x² + 6x + 1 - 4 ( x² - 4x + 4)
= 9x² + 6x + 1 - 4x² + 16x - 16
= 5x² + 22x - 15
= 5x² + 25x - 3x - 15
= 5x ( x + 5) - 3 ( x + 5)
= ( x + 5 ) ( 5x - 3 )
4) 9 ( 2x + 3 )² - 4 ( x - 2)²
= 9 ( 4x² + 12x + 9) - 4 ( x² - 4x + 4)
= 36x² + 108x + 81 - 4x² + 16x - 16
= 32x² + 124x + 65
= 32x² + 104x + 20x + 65
= 8x ( 4x + 13) + 5 ( 4x + 13)
= ( 8x + 5) ( 4x + 13)
NHỚ VOTE 5 SAO VÀ CTLHN CHO MIK NHÉ. THANKS!!!