Упрости выражения

1. \(\sin \left(\dfrac{3\pi}{2}+\alpha \right)\) ;

2. \(\ctg \left(\pi +\alpha \right)\) ;

3. \(\tg \left(\alpha -\pi \right)\) ;

4. \(\cos ^2 \left(\pi -\alpha \right)\) .

Ответ: 1) [ ]; 2) [ ]; 3) [ ]; 4) [ ].