先化简,再求值:3x^3-[x^3+(6x^2-7x)]-2(x^3-3x^2-4x),其中x=-1/3

问题描述:

先化简,再求值:3x^3-[x^3+(6x^2-7x)]-2(x^3-3x^2-4x),其中x=-1/3

3x^3-[x^3+(6x^2-7x)]-2(x^3-3x^2-4x)
=3x^3-x^3-6x^2+7x-2x^3+6x^2+8x
=15x
当x=-1/3时,原式=15*(-1/3)=-5

合并同类项化简得15x

3x^3-[x^3+(6x^2-7x)]-2(x^3-3x^2-4x)
=3x^3-(x^3+6x^2-7x)-2x^3+6x^2+8x
=3x^3-x^3-6x^2+7x-2x^3+6x^2+8x
=15x
=15×(-1/3)
=-5

3x^3-[x^3+(6x^2-7x)]-2(x^3-3x^2-4x)
=3x³-[x³+6x²-7x]-2x³+6x²+8x
=3x³-x³-6x²+7x-2x³+6x²+8x
=15x
=15×(-1/3)
=-5