`(x - y)^3 - (x + y)^3`
`= (x - y - x - y)[(x - y)^2 + (x - y)(x + y) + (x + y)^2]`
`= -2y[(x - y)^2 + (x - y)(x + y) + (x + y)^2]`
`(x + 1)^3 + (x - 1)^3`
`= (x + 1 + x - 1)[(x + 1)^2 + (x + 1)(x - 1) + (x - 1)^2]`
`= 2x[(x + 1)^2 + (x + 1)(x - 1) + (x - 1)^2]`
`x^3 + 1/27`
`= x^3 + (1/3)^3 `
`= (x + 1/3)(x^2 + 1/3x + 1/9)`
`(a^2 + b^2 - 5)^2 - 4(ab + 1)^2`
`= (a^2 + b^2 - 5)^2 - [2(ab + 1)]^2`
`= [a^2 + b^2 - 5 - 2(ab + 1)][a^2 + b^2 - 5 + 2(ab + 1)]`
`= (a^2 + b^2 - 2ab - 5 - 2)(a^2 + b^2 + 2ab - 5 + 2)`
`= [(a - b)^2 - 7][(a + b)^2 - 3]`