x²=3x-1
x四次+3x²+1
=(x^2)^2+3x²+1
=(3x-1)^2+3x²+1
=9x^2-6x+1+3x²+1
=12x^2-6x+2
=12x^2-2(3x-1)
=12x^2-2x^2
=10x^2
原式=x²/10x^2=1/10