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