先化简再求值3x²（2y-x）-3y(2x²+y)其中X= 2/3,y=-1/3
问题描述：
先化简再求值3x²（2y-x）-3y(2x²+y)其中X= 2/3,y=-1/3
答
3x²（2y-x）-3y(2x²+y)
=6x²y-3x^3-6x²y-3y^3
=-3x^3-3y^3
=-3*(2/3)^3-3*(-1/3)^3
=-3*8/27-3*(-1/27)
=-8/9+1/9
=-7/9
答
3x²（2y-x）-3y(2x²+y)
=6x²y-3x³-6x²y-3y²
=-3x³-3y²
=-3(x³+y²)
=-3*[(2/3)³+(-1/3)²]
=-3*[8/27+1/9]
=-3*11/27
=-11/9
答
3x²（2y-x）-3y(2x²+y)
=6x^2y-3x^3-6x^2y-3y^2
=-3(x^3+y^2)
=-3[(2/3)^3+(-1/3)^2]
=-3(8/27+1/9)
=-11/9