a, `x^3` + `x^2` + `x/3` + `1/27`
= `x^3` + 3 . `x^2` . `1/3` + 3 . x . `1/9` + `(1/3)^3`
= `(x + 1/3)^3`
b, `8x^3` + `12x^2` + 6x + 1
= `(2x)^3` + 3 . `4x^2` . 1 + 3 . 2x . `1^2` + `1^3`
= `(2x + 1)^3`
c, `x^3` - `6x^2 y` + `12xy^2` - `8y^3`
= `x^3` - 3 . `x^2` . 2y + 3 . x . `4y^2` - `(2y)^3`
= `(x - 2y)^3`
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