Hello, je vais essayer de t'aider :
E = (2x-5)² - (2x - 5)( -7x+3)
A) Développement : (2x-5)² - (2x-5)(-7x +3) =
(4x²-20x+25) - (-14x² +6x+35x -15 = (4x²-20x+25) -(-14x²+41x-15) =
4x²+14x²-20x-41x+25+15 = 18x² -61x +40
B) (2x-5)² - ( 2x -5)(-7x +3) = (2x-5)(2x-5) - (2x -5)( -7x+3)
= ( 2x -5) [2x-5 +7x-3]
= ( 2x -5) ( 2x+7x-5-3)
= (2x- 5) (9x-8)
C) x = -2 donc tu remplaces x [2 *(-2) - 5 ] [9*(-2) -8] =
[-4-5][-18-8] = (-9)(-26) = 234
D) (2x-5)(9x-8) = 0 alors 2x-5 = 0 soit x = 5/2
alors 9x -8 = 0 soit x = 8/9
E = 0 si x = 5/2 ou x =8/9 ... Bonne journée .. Salut