Ответы и объяснения

2013-11-28T10:03:26+00:00
(1/sina+ctga)(1/sina-ctga)= ((1/sina)^2-(ctga)^2)=
=1/sin^2a-cos^2a/sin^2a=(sin^2a+cos^2a-cos^2a)/sin^2a=sin^2a/sin^2a=1