a)
[tex] - 2( {x}^{ 3} + {2x}^{2} - x) - x( { - 2x}^{2} + 4) + \frac{1}{2} x(6x + 8) = { - 2x}^{3} - {4x}^{2} + 2x + {2x}^{3} - 4x + {3x}^{2} + 4x = { - x}^{2} + 2x[/tex]
b)
[tex]2xy(x - y) - 3x(xy + 1) + 4y(xy - 1) = {2x}^{2} y - 2x {y}^{2} - {3x}^{2} y - 3x + 4x {y}^{2} - 4y = - {x}^{2} y + 2x {y}^{2} - 3x - 4y[/tex]
