To simplify this expression, we can substitute cos^2a with 1-sin^2a:
(1 - (1 - sin^2a) + sin^2a) / (1 + (1 - sin^2a) + sin^2a)(1 - 1 + sin^2a + sin^2a) / (1 + 1 - sin^2a + sin^2a)(2sin^2a) / 2sin^2a
Therefore, the simplified expression is sin^2a.
To simplify this expression, we can substitute cos^2a with 1-sin^2a:
(1 - (1 - sin^2a) + sin^2a) / (1 + (1 - sin^2a) + sin^2a)
(1 - 1 + sin^2a + sin^2a) / (1 + 1 - sin^2a + sin^2a)
(2sin^2a) / 2
sin^2a
Therefore, the simplified expression is sin^2a.