bonjour
A = 2x( 4x _ 7 ) = 8 x² - 14 x
. B = ( 2x _ 9 ) (4x _ 7 ) = 8 x² - 14 x - 36 x + 63 = 8 x² - 48 x + 63
C = ( 2x +3 ) ( 5x _ 1 ) _ 2x (x + 3 ).
C = 10 x² - 2 x + 15 x - 3 - 2 x² - 6 x
= 8 x² + 7 x - 3
D = ( 3x + 1 ) ( 3x _ 1 ) _ ( 3x + 6 ) ( 5x _ 1 ) .
= 9 x² - 1 - ( 15 x² - 3 x + 30 x - 6 )
= 9 x² - 1 - 15 x² + 3 x - 30 x + 6
= - 6 x² - 27 x + 5