3x^2-x-1=0(3x^2-x-1)²=0(3x^2-x-1)²=9x^4-6x³-5x²+2x+1=09x^4+12x^3-3x^2-7x+1999=（9x^4-6x³-5x²+2x+1）+18x³+2x²-9x+1998=18x³+2x²-9x+1998=2001-x²