Giải giúp em với ạ =))

`a, (-1/2 xy)( 2/3 x^2 - 3/4 xy + 4/5 y^2)`

`= -1/2 xy . 2/3 x^2 + 1/2 xy . 3/4 xy - 1/2 xy . 4/5 y^2`

`= -1/3 x^3 y + 3/8 x^2 y^2 - 2/5 xy^3`

`b, 2x^2 . a - a(1+2x^2) - a - x(x+a)`

`= 2ax^2 - a - 2ax^2 - a - x^2 - xa`

`= - 2a - x^2 - xa`

`c, (1/2x - 1)(2x-3)( 4x-1)`

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

`= ( x^2 - 7/2x + 3)(4x-1)`

`= 4x^3 - 14x^2 + 12x - x^2 + 7/2 x - 3`

`= 4x^3 - 15x^2 + 31/2 x -3`