-//- = (cos(a) + sin(a)cos(a) - cos(a) + sin(a)cos(a)) / (1-sin(a))(1+sin(a)) =
2sin(a)cos(a) / (1 - sin²(a)) = 2sin(a)cos(a) / cos²(a) = 2sin(a) / cos(a) = 2tg(a)
-//- = (cos(a) + sin(a)cos(a) - cos(a) + sin(a)cos(a)) / (1-sin(a))(1+sin(a)) =
2sin(a)cos(a) / (1 - sin²(a)) = 2sin(a)cos(a) / cos²(a) = 2sin(a) / cos(a) = 2tg(a)