Respuesta :

[tex] \frac{(1 - \cos(a))(1 + \cos(a)) }{(1 - \sin(a) )(1 + \sin(a)) } = \\ [/tex]

[tex] \frac{1 - {cos}^{2}(a) }{1 - {sin}^{2}(a) } = \\ [/tex]

[tex] \frac{ {sin}^{2}(a) }{ {cos}^{2}(a) } = \\ [/tex]

[tex] {tan}^{2} (a)[/tex]