arctg2*(1/2) - arcsin (1/2)= arctg 1 - arcsin (1/2)= pi/4-pi/6 =pi/12
arctg2*(-1/2) - arcsin (-1/2)= -arctg 1 + arcsin (1/2)= -pi/4+pi/6 =-pi/12
arctg 2* (-sgrt(3))/2 - arcsin (-sgrt(3)/2)= -pi/3 + pi/3=0
arctg 2* (sgrt(3))/2 - arcsin (sgrt(3)/2)= pi/3 - pi/3=0