bonjour
A = ( 3 x + 9 ) ( 2 x - 5 ) - ( 7 x - 8 ) ( 3 x+ 9 )
A = 6 x² - 15 x + 18 x - 45 - ( 21 x² + 63 x - 24 x - 72 )
A = 6 x² + 3 x - 45 - 21 x² - 63 x + 24 x + 72
A = - 15 x² - 36 x + 27
A = ( 3 x + 9 ) ( 2 x - 5 - 7 x + 8 )
A = ( 3 x + 9 ) ( - 5 x + 3 )
A = 0 pour x = - 9/3 = - 3 et pour x = 3/5
A = 27
15 x² - 36 x + 27 = 27
15 x² - 36 x + 27 - 27 = 0
x ( 15 x - 36 ) = 0
x = 0 ou 36/15 = 12/5