Đáp án:
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Giải thích các bước giải:
`a)`
`(a+b)^3+(a-b)^3-2a^2(a+1)`
`=a^3+b^3+3.a^2. b+ 3.ab^2+a^3-3.a^2b+3.ab^3-b^3-2a^3-2a^2`
`=6ab^2-2a^2`
`b)`
`(2x-1)^3-(2x+1)^3-5x(x-3)`
`=8x^3-3.4x^2 .1+3.2x.1^2-1-(8x^3+3.4x^2. 1+3.2x.1^2+1)-5x^2+15`
`=8x^3-12x^2+6x-1-8x^3-12x^2-6x-1-5x^2+15`
`=-29x^2+13`
`c)`
`(x+2)^3+(x-2)^3-2x(x^2+12)`
`=x^3+6x^2+12x+8+x^3-6x^2+12x-8-2x^3-24x`
`=0`
`d)`
`(2a+3b)^3-(2a-3b)^3+3(2a-b)(2a+b)`
`=8a^3+36a^2b+54ab^2+27b^3-(8a^3-36a^2b+54ab^2-27b^3)+3(4a^2-b^2)`
`=8a^3+36a^2b+54ab^2+27b^3-8a^3+36a^2b-54ab^2+27b^3+12a^2-3b^2`
`=72a^2b+54b^3+12a^2-3b^2 .`