去括号合并:(1)3x^3-[x^3+(6x^2-7x)]-2(x^3-3x^2-4x)(2)(3x^2-4y^2)+[-(x^2-2xy-y^2)]-[-(3x-2xy-y^2)]

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去括号合并:(1)3x^3-[x^3+(6x^2-7x)]-2(x^3-3x^2-4x)
(2)(3x^2-4y^2)+[-(x^2-2xy-y^2)]-[-(3x-2xy-y^2)]

(1)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^3-2x^3-6x^2+6x^2+7x+8x
=15x
(2)(3x^2-4y^2)+[-(x^2-2xy-y^2)]-[-(3x-2xy-y^2)]
=3x^2-4y^2-x^2+2xy+y^2+3x-2xy-y^2
=3x^2-x^2-4y^2+y^2-y^2+2xy-2xy+3x
=2x^2-4y^2+3x

3x^3-[x^3+6x^2-7x]-2x^3+6x^2=8x
= 3x^3-x^3-6x^2+7x-2x^3+6x^2=8x
=9x^