Réponse:
1. f(x) = (3x+1)2 - (2x-3)2 de la forme a2-b2 = (a-b)(a+b)
= (3x+1-2x+3)(3x+1+2x-3)
= (x+4)(5x-2)
2. f(x) = x(5x-2) +4(5x-2)
= 5x2 -2x +20x -8
= 5x2 + 18x -8
3. a) f(x) = 0
(x + 4) (5x - 2) = 0
x + 4 = 0 ; 5x - 2 = 0
x = -4 ; x = 2/5
b) image de -4 par f
(-4+4)(5×-4-2) = 0
c) f(x) = -8
5x2 + 18x -8 = -8
5x2 + 18x = 0
x(5x + 18) = 0
x = 0 ; 5x + 18 = 0
x = -18/5
