x^4-3x2+1 =x^4-2X²+1-X²=（X²-1)²-X²=(X²+X-1)(X²-X-1)x^4+2x2+9 ==x^4+6X²+9-4X²=(X²+3)²-(2x)²=(X²+2X+3)(X²-2X+3)