\(\tan\cfrac{3\pi}{20} \cdot \tan\cfrac{4\pi}{20} \cdot \tan\cfrac{5\pi}{20} \cdot \tan\cfrac{6\pi}{20} \cdot \tan\cfrac{7\pi}{20}\)
=\(\tan\cfrac{3\pi}{20} \cdot \tan\cfrac{4\pi}{20} \cdot \tan\cfrac{\pi}{4}\)
\(\cdot\cot(\cfrac{\pi}{2}-\cfrac{6\pi}{20})\) \(\cdot\cot(\cfrac{\pi}{2}-\cfrac{7\pi}{20})\)
=\(\tan\cfrac{3\pi}{20} \cdot \tan\cfrac{4\pi}{20} \cdot \tan\cfrac{\pi}{4}\)\(\cdot\cot(\cfrac{10\pi-6\pi}{20})\) \(\cdot\cot(\cfrac{10\pi-7\pi}{20})\)
=\(\tan\cfrac{3\pi}{20} \cdot \tan\cfrac{4\pi}{20} \cdot \tan\cfrac{\pi}{4}\)\(\cdot\cot \cfrac{4\pi}{20} \) \(\cdot\cot \cfrac{3\pi}{20} \)
=\(\tan\cfrac{3\pi}{20} \cdot \cot \cfrac{3\pi}{20} \times \tan\cfrac{4\pi}{20} \cot \cfrac{4\pi}{20} \)\(\times \tan\cfrac{\pi}{4}\)
=\(1 \times 1 \times 1\)=\(1\) (Answer).