x³+4x²+x+4=0 x²(x+4)+(x+4)=0 (x²+1)(x+4)=0 x=-4
x³+4x²+x+4=0 x³+x+4x²+4=0 x(x²+1)4(x²+1)=0 (x+4)(x²+1)=0 x=-4 ∨ x²=-1