Réponse:
[tex] \sin(90 - \beta ) = \cos(90) [/tex]
[tex] \tan(y) \times \sqrt{1 + \sin(y) } \times \sqrt{1 - \sin(y) } - \sin(y)[/tex]
[tex] \tan(y) \times \sqrt{(1 {}^{2} } + \sin {}^{2} y) - \sin(y) [/tex]
[tex]tan(y) \times \sqrt{ \cos {y}^{2} ) } - \sin(y) [/tex]
[tex] \frac{ \sin(y) }{ \cos(y) } \times \cos(y) - \sin(y) [/tex]
[tex] \sin(y) - \sin(y) [/tex]
[tex] = 0[/tex]
