若3x^2-x-1=0,求9x^4+12x^3-3x^2-7x+1999的值

问题描述:

若3x^2-x-1=0,求9x^4+12x^3-3x^2-7x+1999的值

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