x²+3X+1=0∴x+3+1/x=0 两边除以xx+1/x=-3 (x-1/x)²=x²-2+1/x²=(x+1/x)²-4=9-4=5∴x-1/x=√5或-√5 3x³+7x²-3x+6=3x³+9x²+3x-2x²-6x-2+8=3x(x²+3X+1)-2(x²+3X+1)+8∵x²+3X+1=0∴原式=8
