Помогите решить уравнение x^4+5x^3+5x^2-5x-6=0

x^4+5*x^3+5x^2-5x-6=0 (x^4-1)+5*x^2(x+1)-5*(x+1)=0 (x^2+1)*(x-1)*(x+1)+5*x^2*(x+1)-5*(x+1)=0 (x+1)* ( (x^2+1)*(x-1)+5*x^2-5)=0 (x+1)*( (x^2+1)*(x-1)+5*(x-1)*(x+1))=0 (x+1)*(x-1)*(x^2+5x+6)=0 (x+1)*(x-1)*(x+2)*(x+3)=0 x1=1 x2=-1 x3=-2 x4=-3