x^2+4x-1=0
x²+4x=1
3x^4+12x^3-6x^2-12x+2
=3x²(x²+4x)-6x²-12x+2
=3x²-6x²-12x+2
=-3x²-12x+2
=-3(x²+4x)+2
=-3+2
=-1