3x^2-x=1
9x^4-6x^3+7x^2-2x+999
=9x^4-3x^3-3x^3+x^2+6x^2-3x+999
=3x^2(3x^2-x)-x(3x^3-x)+2(3x^2-x)+999
=3x^2*1-x+2*1+999
=3x^2-x+2+999
=1+1001
=1002