Răspuns :
(3x+1)² - (x+3)² = ( 3x + 1 + x +3) · ( 3x +1 -x - 3) =
= ( 4x + 4) · ( 2x - 2 ) =
= 4 · ( x +1) ·2 · ( x -1 ) =
= 8 · ( x +1 ) · ( x - 1)
= ( 4x + 4) · ( 2x - 2 ) =
= 4 · ( x +1) ·2 · ( x -1 ) =
= 8 · ( x +1 ) · ( x - 1)