Phân tích thành nhân tử 

- Hướng dẫn giải

$$\begin{gathered} abc -(ab+bc+ca) + (a+b+c) -1 \\ =abc-ab-bc-ca+a+b+c-1 \\ =abc-bc-ab+b-ca+c+a-1 \\ =bc\left(a-1\right)-b\left(a-1\right)-c\left(a-1\right)+\left(a-1\right) \\ =\left(a-1\right)\left(bc-b-c+1\right) \\ =\left(a-1\right)\left[c\left(b-1\right)-\left(b-1\right)\right] \\ =\left(a-1\right)\left(b-1\right)\left(c-1\right) \end{gathered}$$