sin(-x_):= -sin(x);
sin(pi/2+x_):= cos(x);
sin(pi/2-x_):= cos(x);
sin(asin(x_)):=x;
sin(pi) := 0;
sin(2pi):=0;
sin(2pi+x_):=sin(x);
sin(-2pi+x_):=sin(x);