@article{NAM_1844_1_3__456_0,
     author = {Vignal},
     title = {D\'emonstration g\'eom\'etrique de la formule de trigonom\'etrie $\frac{b+c}{b-c}=\frac{\tan \frac{1}{2}(B+C)}{\tan \frac{1}{2}(B-C)}$},
     journal = {Nouvelles annales de math\'ematiques : journal des candidats aux \'ecoles polytechnique et normale},
     pages = {456--457},
     publisher = {Carilian-Goeury et Vor Dalmont},
     volume = {1e s{\'e}rie, 3},
     year = {1844},
     language = {fr},
     url = {http://www.numdam.org/item/NAM_1844_1_3__456_0/}
}