câu 1 a,(x-3)^3-(x-2)^3 b,(5x-2y)^2-(x+3y)^#-(2x+y)^2 câu 2 rút gọn A=(3x-y)^2-(x+2y)*(x^2-2xy+4y^2)+(3x)^2

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1. `1a,(x-3)^3-(x-2)^3`

   `=(x-3-x+2)[(x-3)^2+(x-3)(x-2)+(x-2)^2]`

   `=-(x-3)^2-(x-3)(x-2)-(x-2)^2`

   `=x^2-6x+9-x^2+5x-6-x^2+4x-4`

   `=(-6x+5x+4x)+(9-6-4)+x^2`

   `=-x^2+3x-1`

   Vậy ………………..

   `b,(5x-2y)^2-(x+3y)^3-(2x+y)^2`

   `=25x^2-20xy+4y^2-x^3-9x^2y-27xy^2-27y^3-4x^2-4xy-y^2`

   `=x^3-9x^2y-27xy^2-27y^3+21x^2-24xy+3y^2`

   Vậy ………………..

   `2,A=(3x-y)^2-(x+2y)*(x^2-2xy+4y^2)+(3x)^2`

   `A=9x^2-6xy+y^2-x^3-8y^3+9x^2`

   `A=-x^3-8y^3+18x^2-6xy+y^2`

   Vậy ………………..

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2. Đáp án:

   `1a,=-x^2+3x-1`

   `b,=x^3-9x^2y-27xy^2-27y^3+21x^2-24xy+3y^2`

   `2,A=-x^3-8y^3+18x^2-6xy+y^2`

   Giải thích các bước giải:

   `1a,(x-3)^3-(x-2)^3`

   `=(x-3-x+2)[(x-3)^2+(x-3)(x-2)+(x-2)^2]`

   `=-(x-3)^2-(x-3)(x-2)-(x-2)^2`

   `=x^2-6x+9-x^2+5x-6-x^2+4x-4`

   `=-x^2+3x-1`

   `b,(5x-2y)^2-(x+3y)^3-(2x+y)^2`

   `=25x^2-20xy+4y^2-x^3-9x^2y-27xy^2-27y^3-4x^2-4xy-y^2`

   `=x^3-9x^2y-27xy^2-27y^3+21x^2-24xy+3y^2`

   `2,A=(3x-y)^2-(x+2y)*(x^2-2xy+4y^2)+(3x)^2`

   `=9x^2-6xy+y^2-x^3-8y^3+9x^2`

   `=-x^3-8y^3+18x^2-6xy+y^2`

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