sen x -1 -cos^2x
------------ = --------------------
senx +1 (senx +1)^2
(senx -1)(senx +1) -cos^2x aplicando (a +b)(a -b) = a^2 -b^2
------------------------------ = ----------------
(senx +1)( senx +1) ( senx +1)^2
sen^2 -1 -cos^2x como sen^2x = 1-cos^2x remplazo
---------------------------- = -------------------
(senx +1)^2 (senx +1)^2
1 - cos^2x -1 -cos^2x
---------------------- = -----------------
( senx +1 )^2 (senx + 1)^2
-cos^2x -cos^2x
-------------------- = ----------------
( senx +1)^2 (senx +1 )^2
