x³-3x²+x+2=0x³-2x²-x²+x+2=0x²(x-2)-(x²-x-2)=0x²(x-2)-(x+1)(x-2)=0(x²-x-1)(x-2)=0x²-x-1=0x²-x+ 1/4 =5/4(x-1/2)^2=5/4x-1/2 =±√5/2x=(1±√5)/2所以 x=(1±√5)/2 或 x=2