А)sina * ctga + cosa= sina8 cosa/sina +cosa= cosa + cosa= 2cosa
б)1/sin^2a -1/tg^2a= tg^2a/sin^2 -sin^2a/tg^2a= tg^2a-sin^2a/sin^2a * tg^2a=sin^2a-sin^2a * cos^2a/sin^2a * cos^2a= sin^2a(1-cos^2a)/sin^2a * cos^2a= sin^2 a/ cos^2a=ctg^2a
в)1+cosa/1-cosa - 1+2cosa/sin=