Đề bài

Tính:

a) $\frac{1}{4}x.\left( {\frac{1}{2}{x^2}} \right).\left( { - \frac{4}{5}{x^3}} \right)$                                        b) $0,5{x^{m + 1}}.0,8{x^{m - 1}}(m \in \mathbb{N},m \ge 1)$

c) $\left( {{x^3} - 3x + \frac{1}{4}} \right)( - 3{x^3})$                                          d) $(x - 2)({x^2} + x - 1) - x({x^2} - 1)$