Réponses

  • Utilisateur Brainly
2013-06-23T21:40:16+02:00

(cos(ABC))²+(cos(ACB))²

=cos²(B)+sin²(C)

=AE²/EF²+AF²+EF²

=EF²/EF²

=1

 

car cos(ABC)=sin(90°-ACB)=sin (ACB)