对不等式变形有[x-x^2+7x-12]/(x^2-7x+12)>=0,又因为x^2-7x+12=(x-3)(x-4)-x^2+8x-12=-(x-2)(x-6),于是有-(x-2)(x-3)(x-4)(x-6)>=0于是解得2=
