X³-3X²-5X-1=0
X³-3X²-5X-1=X³-3X²-4X-(X+1)=X(X-4)(X+1)-(X+1)
=(X+1)(X²-4X-1)=(X+1)[(X-2)²-5]=0
X1=-1,X2=2+√5,X3=2-√5