Помогитеееее!!!!!!!!! вычислить tg20*tg40*tg60*tg80

Решите задачу:

$Formyla:\\\\\star \; \; tg \alpha \cdot tg(60^\circ - \alpha )\cdot tg(60^\circ + \alpha )=tg3 \alpha \; \\\\( \alpha \ne 180^\circ n\pm 30^\circ ,\; \alpha \ne 180^\circ n +90^\circ \; )\; \; \star \\\\\\tg20^\circ \cdot tg(60^\circ -20^\circ )\cdot tg(60^\circ +20^\circ )=tg20^\circ \cdot tg40^\circ \cdot tg80^\circ =\\\\=tg(3\cdot 20^\circ )=tg60^\circ =\sqrt3\\\\\\tg20\cdot tg40\cdot tg60\cdot tg80=tg60\cdot tg60=tg^260=(\sqrt3)^2=3$