Вычислите arcctg0,5 - arctg (-1/3)

arctga+arctgb=arctg (a+b) / (1-ab)

arctg (-a) = - arctga

Вот и все формулы, которые нам нужны

arctg0,5-arctg (-1/3) = arctg0,5+arctg (1/3) = arctg (1/2) + arctg (1/3) =

=arctg (1/2 + 1/3) / (1 - 1/2*1/3) =

=arctg (5/6) / (1-1/6) = arctg (5/6) / (5/6) = arctg1=π/4