Répondre :
sin ( pi /2 - 5pi /6 ) +cos( pi /2- pi /3)
=cos(-5pi/6)+sin(pi/3)
=cos(5pi/6)+sin(pi/3)
=-cos(pi/6)+rac(3)/2
=-rac(3)/2+rac(3)/2
=0
=cos(-5pi/6)+sin(pi/3)
=cos(5pi/6)+sin(pi/3)
=-cos(pi/6)+rac(3)/2
=-rac(3)/2+rac(3)/2
=0