Упростите выражение tga-sina/tga+sina

tg a = sin a/cos a

sin a/cos a - sin a / sin a/cos a + sin a=

= (sin a-sin a cos a) / cos a / (sin a+sin a cos a) / cos a=

=sin a (1-cos a) / sin a (1+cos a) =

= (1-cos a) / (1+cos a)