coucou
formule du cours
sin x = sin (π-x)
donc sin 3π/8 = sin (π-3π/8) =sin (8π/8 -3π/8)
=sin (5π/8)
et
sin π/8 = sin (π-π/8) =sin (8π/8 -π/8)
=sin (7π/8)
donc on a
sin π/8 - sin 3π/8 + sin 5π/8 - sin 7π/8
= sin π/8 - sin 3π/8 + sin 3π/8 - sin π/8
= sin π/8 - sin π/8 - sin 3π/8+ sin 3π/8
= 0
