1. Calculate: $143 \cdot 91 \cdot 77-\sqrt{143} \cdot \sqrt{91} \cdot \sqrt{77}$.
1. Calculate: $143 \cdot 91 \cdot 77-\sqrt{143} \cdot \sqrt{91} \cdot \sqrt{77}$.

## Solution.

$$
\begin{aligned}
& 143 \cdot 91 \cdot 77-\sqrt{143} \cdot \sqrt{91} \cdot \sqrt{77} \\
& =11 \cdot 13 \cdot 7 \cdot 13 \cdot 7 \cdot 11-\sqrt{11} \cdot \sqrt{13} \cdot \sqrt{7} \cdot \sqrt{13} \cdot \sqrt{7} \cdot \sqrt{11} \\
& 1 \text{ POINT} \\
& =(11 \cdot 13 \cdot 7)^{2}-(\sqrt{11} \cdot \sqrt{13} \cdot \sqrt{7})^{2} \\
& 1 \text{ POINT} \\
& =1001^{2}-(\sqrt{1001})^{2} \\
& 1 \text{ POINT} \\
& =1001^{2}-1001 \\
& 1 \text{ POINT} \\
& =1001 \cdot(1001-1) \\
& 1 \text{ POINT} \\
& =1001 \cdot 1000 \\
& =1001000
\end{aligned}
$$