bonjour
f(x) = ( x + 7) ( 3 x + 21 - 16 x + 12 ) = ( x + 7) ( - 13 x + 33)
f(x) = 3 ( x² + 14 x + 49) - 4 ( 4 x ² - 3 x + 28 x - 21 )
= 3 x² + 42 x + 147 - 16 x² + 12 x - 112 x + 84
= - 13 x² - 58 x + 231
( x + 7) ( - 13 x + 33 )
= - 13 x² + 33 x - 91 x+ 231
= - 13 x² - 58 x + 231