Réponses

2014-08-18T10:25:26+02:00
Cotg(7π/8)=cos(7π/8)/sin(7π/8)
Or 7π/8=3π/8+π/2
donc cos(7π/8)=cos(3π/8+π/2)=-sin(3π/8)
et sin(7π/8)=sin(3π/8+π/2)=cos(3π/8)
Donc cotg(7π/8)=-sin(3π/8)/cos(3π/8)=-tg(3π/8)
On en déduit que :
tg(3π/8)/cotg(7π/8)=-1