一、原式=2x^2-2x-[x-6x^3-3x^2+3x]-6x^2
=2x^2-2x-x+6x^3+3x^2-3x-6x^2
=6x^3-x^2-6x
=6x(-1/8)-(1/4)+3
=(-3/4)+(-1/4)+3
=2
二、(1)原长方体体积是 4x4x5=80cm^3
(2)新体积为:5(4+x)(4-x)=80-5x^2
(3) 因为5x^2>0,所以 80-5x^2
一、原式=2x^2-2x-[x-6x^3-3x^2+3x]-6x^2
=2x^2-2x-x+6x^3+3x^2-3x-6x^2
=6x^3-x^2-6x
=6x(-1/8)-(1/4)+3
=(-3/4)+(-1/4)+3
=2
二、(1)原长方体体积是 4x4x5=80cm^3
(2)新体积为:5(4+x)(4-x)=80-5x^2
(3) 因为5x^2>0,所以 80-5x^2