Заполни пропуски в решении

Вычисли значения \(\cos \alpha\) и \(\ctg \alpha\) , если:

1. \(\sin \alpha = \dfrac{3}{4}\) и \(0 \degree \lt \alpha \lt 90 \degree\) ;
2. \(\sin \alpha = \dfrac{5}{9}\) и \(90 \degree \lt \alpha \lt 180 \degree\) .

Решение.

1. \(\cos^2 \alpha = \) [ ] \(=\) [ ] \(=\) [ ]. \(\cos \alpha\) [ ] \(0\) , так как \(0 \degree \lt \alpha \lt 90 \degree\) . Следовательно, \(\cos \alpha =\) [ ]. \(\ctg \alpha = \) [ ] \( = \) [ ] \( = \) [ ].

2. \(\cos^2 \alpha =\) [ ] \( = \) [ ] \( = \) [ ].

      Отметим, что  \(\cos \alpha\) [ ] \(0\) , так как  \(90 \degree \lt \alpha \lt 180 \degree\)  ( по        [ ]). Следовательно,  \(\cos \alpha = \) [ ],  \(\ctg \alpha = \) [ ] \(=\) [ ] \(=\) [ ].
   

Ответ:

1. \(\cos \alpha = \) [ ], \(\ctg \alpha =\) [ ];
2. \(\cos \alpha = \) [ ], \(\ctg \alpha =\) [ ].