Вычисли

а) \(\tg \left(\arcctg\left(-\dfrac{7}{8}\right)\right) =\) [ ];

б) \(\ctg \left( \arctg \dfrac{13}{12} \right)= \) [ ];

в) \(\sin \left( \arctg \dfrac{12}{5} \right) = \) [ ];

г) \(\cos \left( \arcctg \left( - \dfrac{15}{8} \right) \right) = \) [ ].