Thu gọn các đa thức sau:(a) 2x^2yz + 4xy^2z – 5x^2yz + xy^2z – xyz;(b) x^3 - 5xy + 3x^3 + xy - x^2 + 1/2xy - x^2

a) 2x²yz + 4xy²z – 5x²yz + xy²z – xyz

= (2x²yz – 5x²yz) + (4xy²z + xy²z) – xyz

= (2 – 5)x²yz + (4 + 1)xy²z – xyz

= –3x²yz + 5xy²z – xyz

b) \({x^3} - 5xy + 3{x^3} + xy - {x^2} + \frac{1}{2}xy - {x^2}\)

\( = \left( {{x^3} + 3{x^3}} \right) + \left( {xy + \frac{1}{2}xy - 5xy} \right) - \left( {{x^2} + {x^2}} \right)\)

\( = 4{x^3} - \frac{7}{2}xy - 2{x^2}\).