Упрости выражения

1. \(\cos \left(\pi +\alpha \right)\) ;

2. \(\ctg \left(\dfrac{\pi}{2} -\alpha \right)\) ;

3. \(\tg \left(\alpha -\dfrac{3\pi}{2} \right)\) ;

4. \(\tg ^2 \left(\dfrac{5\pi}{2}-\alpha \right)\) .

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