а) arcctg (-1)+arctg корень из 3/3 - arcctg 0 б) ctg (arccos 1/корень из 2) в)arcctg (cos...

============ a ============

$arcctg (-1)+arctg \frac{ \sqrt{3} }{3} - arcctg 0 = \frac{3 \pi }{4} + \frac{ \pi }{6} - \frac{ \pi }{2} = \frac{9 \pi +2 \pi -6 \pi }{12} = \frac{5 \pi }{12}$

============ б ============

$ctg (arccos \frac{1}{ \sqrt{2} } ) = ctg \frac{ \pi }{4} =1$

============ c ============

$arcctg (cos \pi )=arcctg (-1)= \frac{3 \pi }{4}$