1) arcsin0 = 0
2) arccos (-1/2) = 2π/3
3) arctg√3 = π/3
4) arcctg√3/3 = π/3
5) arcsin1+ arccos 1 = π/2
6) tg(arctg√2)*ctg(arctg√2) = √2 · 1/tg(arctg√2) = √2 · 1/√2 = 1
7) arccos(-√2/2)+ arctg(-√3) = 3π/4 - π/3 = 5π/12
8) ctg(arccos4/5) = 4/5 ÷ √1-(4/5)² = 4 ÷ 5√1-(4/5)² = 4 ÷ 5√1-16/25 = 4 ÷ 5√9/25 = 4 ÷ 5 · 3/5 = 4/3