x²+3x=6
x²=-3x+6
x³=x*x²=x(-3x+6)=-3x²+6x
于是
x³+x²-12x+10
=-3x²+6x+x²-12x+10
=-2x²-6x+10
=-2(x²+3x)+10
=-2*6+10
=-2