(x+4)x = (x²+2x-8)(x+3)
x²+4x= x³+2x²-8x+3x²+6x-24
x²+4x= x³ +5x² -2x-24
x³+5x²-2x-24-x²-4x=0
x³+4x²-6x-24 =0
x²(x+4) -6(x+4) =0
(x+4)(x²-6) =0
(x+4)(x-√6)(x+√6) =0
x+4=0
x₁=-4
x-√6=0
x₂= √6
x+√6=0
x₃=-√6
x(x²-x-6) = x²-9
x³-x²-6x=x²-9
x³-x²-6x-x²+9= 0
x³-2x²-6x+9=0
x³+x²-3x -3x²-3x+9=0
x(x²+x-3) -3(x²+x-3)=0
(x-3)(x²+x-3)=0
x-3=0
x₁=3
x²+x-3=0
D= 1²-4*1*(-3) = 1+12=13
x₂= (-1-√13)/(2*1) = (-1-√13)/2
x₃=(-1+√13)/2