Factoriser, c´est comme j´ai fait, bande de naab.
Je récapitule :
( x + 1 ) ( 4x + 9 ) - 5 ( x + 1 ) = ( x + 1 ) [ ( 4x + 9 ) - 5 x 1 ]
( x + 1 ) ( 2x + 4 ) - ( x - 7 ) ( x + 1 ) = ( x + 1 ) [ ( 2x +4 ) - ( x - 7 ) ]
2 ( x + 1 ) ( x - 4 ) + 3 ( x + 1 ) ( x + 8 ) = ( x + 1 ) [ 2 ( x - 4) + 3 ( x + 8 ) ]
7 ( x + 1 ) ( 2x + 1 ) - 2 ( x - 1 ) ( 3x - 4 ) = ( x + 1 ) [ 7 ( 2x + 1 ) - 2 ( 3x - 4 ) ]
2 ( x + 8 ) ( x + 1 ) + x + 1 = ( x + 1 ) [ 2 ( x + 8 ) + 1 ]
( x + 1 )² + ( x + 1 ) ( x - 4 ) = ( x + 1 ) [ ( x + 1 ) + ( x - 4 )
Si faut factoriser, c´est ça. 