`# Ly`

`a)`

`(2x^3  - 4xy)^3`

`= (2x^3)^3 - 3. (2x^3)^2 . 4xy + 3. 2x^3 . (4xy)^2 - (4xy)^3`

`= 8x^9 - 48x^7y + 96x^5y^2 - 64x^3y^3`

`b)`

`(6x + 1/2)(36x^2 - 3x + 1/4)`

`= (6x + 1/2)[(6x)^2 - 6x . 1/2 + (1/2)^2]`

`= (6x)^3 + (1/2)^3`

`= 216x^3 + 1/8`

`c)`

`(x-5y^2)(x^2 + 5xy^2 + 25y^4)`

`= (x-5y^2)[x^2 + x. 5y^2 + (5y^2)^2]`

`= x^3 - (5y^2)^3`

`= x^3 - 125y^6`