a)
( 3 x + 1 ) ²- ( x + 3 )² =
= 9 x² + 6 x + 1 - ( x² + 6 x + 9 ) =
= 9 x ² + 6 x + 1 - x² - 6 x - 9 =
= 8 x² - 8 =
= 8 ( x² - 1 ) =
= 8 ( x + 1 ) ( x - 1 )
____________________
b)
( 3 x + 5 )² - ( x + 1 )² =
= 9 x² + 30 x + 25 - ( x² + 2 x + 1 ) =
= 9 x² + 30 x + 25 - x² - 2 x - 1 =
= 8 x² + 28 x + 24 =
= 4 × ( 2 x² + 7 x + 6 )
