Respuesta :

silirobert15

[tex]12 = \frac{1+a}{1-a} => 12(1-a)= 1+ a \\=> 12 -12a = 1 + a => 12a+1 = 12-1 \\=> 13a = 11 => a= \frac{11}{13}[/tex]

ok done. Thank to me :>