Bonjour !
1) A(x) = (x+2)² - 9 = x² + 4x + 4 - 9 = x² + 4x - 5
2)A(x) = (x+2)² - 9 = (x+2)²-3² = (x+2+3)(x+2-3) = (x+5)(x-1)
3)
a) A(3) = (3+5)(3-1) = 8*2 = 16.
A(√3-2) = (√3-2 +5)(√3-2 -1) = (√3 +3)(√3 -3) = (√3)² - 3² = 3 - 9 = -6
b) (x+5)(x-1) = 0
x1: x+5 = 0 <=> x = 0-5 = -5, x2: x-1 = 0 <=> x = 0+1 = 1.
c) A(x) = -5
<=> x² + 4x -5 = -5
<=> x² + 4x = 0
<=> x(x+4) = 0
x1: x = 0, x2: x+4 = 0 <=> x = 0-4 = -4.
Voilà, j'espère t'avoir aidé.
