Bonjour ,
1.
F = (4-5x) (2x+3) - (4-5x) (10+x)
F = 8x + 12 - 10x² - 15x - ( 40 + 4x - 50x - 5x² )
F = -10x² - 7x + 12 - 40 - 46x + 5x²
F = -5x² - 53x - 28 .
2.
F = (4-5x) (2x+3) - (4-5x) (10+x)
F = (4-5x) [ (2x+3) - (10+x) ]
F = (4-5x) [ 2x + 3 - 10 - x ]
F = (4-5x) (x-7)
3.
F = (4-5x) (x-7) = 0
soit 4-5x = 0 ou x-7 = 0
-5x = -4 x = 7
x = -4/-5
F = -5x² - 53x - 28 = -28
-5x² - 53x = -28 + 28
-5x² - 53x = 0
x(-5x-53) = 0
soit x = 0 ou -5x-53 = 0
-5x = 53
x = 53/-5
