Hello,
x⁴ + 12x³ - 64x² = 0
x²(x² + 12x - 64) = 0
x² = 0 or x² + 12x - 64 = 0
x = 0
∆ = b² - 4ac = 12² - 4 × 1 × (-64) = 400
x1 = (-b -√∆)/2a = (-12 - 20)/2 = -32/2 = -16
x2 = (-b + √∆)/2a = (-12 + 20)/2 = 8/2 = 4
S = {-16 ; 0 ; 4 }
→ factorizacion de x⁴ + 12x³ - 64x² : x(x - 4)(x + 16)
