So sánh: 

- Hướng dẫn giải

$$\begin{gathered} \begin{array}{l}A=\left(-9\right).\left(-3\right)+21.\left(-2\right)+25\\ A=27+\left(-42\right)+25\\ A=27+25+\left(-42\right)=10\end{array} \\ \begin{array}{l}B=\left(-5\right)\left(-13\right)+\left(-3\right).\left(-7\right)-80\\ B=65+21-80\\ B=86-80=6\end{array} \end{gathered}$$

Vậy A > B