Rút gọn biểu thức sau a,B=(xy+2)^3-6(xy-2)^2+12(xy+2)-8 b,A=(x-3)(x^2+3x+9)-(x^3+3) c,B=(2x-1)(4x^2-2x+1)-8(x+1/2)(x^2-1/2x+1/4) d,C=(x+2y)(x^2-2xy+4y^2)-(2y-3x)(4y^2+6xy+9x^2)

`B= (xy + 2) ^ 3 -6.(xy-2)^ 2 +12.(xy+2)- 8=(xy+2)^ 3 -3. (xy - 2) ^ 2 * 2 +3.(xy-2).2^ 2- 2 ^ 3= (xy + 2 - 2) ^ 3= (xy) ^ 3= x ^ 3 * y ^ 3`

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`A=(x-3). (x ^ 2 + 3x + 9) - (x ^ 3 + 3)=(x-3). (x ^ 2 + x * (3 + 3 ^ 2)) - x ^ 3 - 3= x ^ 3 - 3 ^ 3 - x ^ 3 - 3= - 30`

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`B=(2x-1). (4x ^ 2 - 2x + 1) -8.(x+ 1 /2 ). (x ^ 2 - 1/2 * x + 1/4)=(2x-1). [(2x) ^ 2 - 2x * 1 + 1 ^ 2] - 8.(x+ 1/ 2 )*[x^ 2 -x. 1/2 + (1/2) ^ 2 ]= (2x) ^ 3 - 1 ^ 3 -8.[x^ 3 +( 1 /2 )^ 3 ]=8x^ 3 -1-8. (x ^ 3 + 1/8)= 8x ^ 3 - 1 - 8x ^ 3 - 1=-2`

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`C=(x+2y). (x ^ 2 - 2xy + 4y ^ 2) - (2y - 3x). (4y ^ 2 + 6xy + 9x ^ 2)=(x+2y). [x ^ 2 - x * 2y + (2y) ^ 2] - (2y - 3x)[(2y) ^ 2 + 2y * 3x + (3x) ^ 2]= x ^ 3 + (2y) ^ 3 - [(2y) ^ 3 - (3x) ^ 3]= x ^ 3 + 8y ^ 3 - (8y ^ 3 - 27x ^ 3)= x ^ 3 + 8y ^ 3 - 8y ^ 3 + 27x ^ 3= 28x ^ 3`

`@Ngocnhuy`le