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\(sin 3\alpha = 3sin \alpha - \) [ ];

\(cos 3\alpha = 4cos^3 \alpha - \) [ ];

[ ] \( = \dfrac {3tg \alpha - tg^3 \alpha}{1- tg^2 \alpha}\) ;

[ ] \( = \dfrac {3 ctg \alpha - ctg^3 \alpha}{1 - ctg^2 \alpha}\) .

Пример.

Вычисли:

\(4 cos^3 10^{\circ} - 3cos 10^{\circ} = \) [ ] \(= \) [ ];

\(3 sin 20^{\circ} - 4sin^3 20^{\circ} = \) [ ] \(= \) [ ];

\( \dfrac {3tg 15^{\circ} - tg^3 15^{\circ}}{1- tg^2 15^{\circ}} = \) [ ] \( = \) [ ].