Làm tính nhân a) 2x(x^2 -3) b) (5x-2y)(x^2 -xy+1) c) (x+1)(x-1)(x+2)

* Hướng dẫn giải

a) $2x.(x^2-3) =2{\text{x}}^3-6\text{x}$

b) $\left(5x–2y\right).(x^2–xy+1)$$=5{\text{x}}^3-5x^{2}y+5\text{x}-2{\text{x}}^{2}y+2\text{x}{y}^2-2y$$=5{\text{x}}^3-5x^{2}y+5\text{x}-2{\text{x}}^{2}y+2\text{x}{y}^2-2y$

c) $\left(x+1\right)\left(x–1\right)\left(x+2\right)$$=\left(x^2-1\right)\left(x+2\right)=x^3+2{\text{x}}^2-x-2$