Bonjour,
1) Développer A :
A = (12x+7)²-(11-5x)(12x+7)
↳ Identité remarquable : (a+b)² = a²+2ab+b²
A = 144x²+168x+49-(11-5x)(12x+7)
A = 144x²+168x+49-(132x+77-60x²-35x)
A = 144x²+168x+49-(97x+77-60x²)
A = 144x²+168x+49-97x-77+60x²
A = 204x²+168x+49-97x-77
A = 204x²+71x+49-77
A = 204x²+71x-28
2) Factoriser A :
A = (12x+7)²-(11-5x)(12x+7)
A = (12x+7)(12x+7-(11-5x))
A = (12x+7)(12x+7-11+5x))
A = (12x+7)(17x+7-11)
A = (12x+7)(17x-4)
3) Calculer A pour x = -5/12
A = (12x+7)²-(11-5x)(12x+7)
A = (12×-5/12+7)²-(11-5×-5/12)(12×-5/12+7)
A = (-5+7)²-(11+25/12)(-5+7)
A = 2²-(11+25/12)(-5+7)
A = 2²-157/12×(-5+7)
A = 2²-157/12×2
A = 2²-157/6
A = 4-157/6
A = -133/6
/ = fraction.
Bonne journée.
