#-sin((4pi)/3)= ?#
#((4pi)/3)=pi+pi/3#
#sin(a+b)=sin a*cos b+cos a*sin b#
#sin(pi+pi/3)=sin pi*cos pi/3+cos pi*sin pi/3#
#sin pi=0#
#cos pi=-1#
#sin( pi/3)=sqrt3/2#
#cos(pi/3)=1/2#
#-sin((4pi)/3)=0*1/2-1*sqrt3/2#
#-sin((4pi)/3)=-sqrt3/2#
#"solution :"sqrt3/2#