$\text{@su}$
Giải thích chi tiết:
`B7`:
`1`, `(x - 2)^3 - x(x^2 - x + 1) + 5x^2 + 8`
`= (x - 2)^3 - x^3 + x^2 - x + 5x^2 + 8`
`= -8 + 6x^2 - x + 8`
`= 6x^2 - x`
`2`, `(x + 3)^2 - 9(x + 1)^2 - 9x + 1`
`= x^2 + 6x + 9 - 9(x^2 + 2x + 1) - 9x + 1`
`= x^2 + 6x + 9 - 9x^2 - 18x - 9 - 9x + 1`
`= -8x^2 - 21x + 1`
`B8`:
`1`, (3x - 1)^3 + 8 = 0
`<=>` `(3x - 1)^3 = 8`
`<=>` `(3x - 1)^3 = 2^3`
`<=>` `3x - 1 = 2`
`<=>` `3x = 3`
`<=>` `x = 1`
`2`, `x^3 - 3x^2 + 3x - 2 = 0`
`<=>` `x^3 - 3x^2 + 3x - 1 = 1`
`<=>` `(x - 1)^3 = 1`
`<=>` `x - 1 = 1`
`<=>` `x = 2`
`3`, `(7 + 2x)^3 - 27 = 0`
`<=>` `(7 + 2x)^3 = 27`
`<=>` `(7 + 2x)^3 = 3^3`
`<=>` `7 + 2x = 3`
`<=>` `2x = -4`
`<=>` `x = -2`
`4`, `8x^3 + 12x^2 + 6x + 28 = 0`
`<=>` `(2x)^3 + 3.4x^2 + 3.2x + 3^3 = -1`
`<=>` `(2x + 3)^3 = -1`
`<=>` `2x + 3 = -1`
`<=>` `2x = 2`
`<=>` `x = 1`
$\text{@Bulletproof Boy Scout}$
