1) (tg(90-a)+tga)/(tg(90-a)-tga)=(ctga+tga)/(ctga-tga)
2) sin^2(a/2+2b)-sin^2(a/2-2b)=1/2[cos(a-4b)-cos(a+4b)]=
=sin(a-4b+a+4b)/2sin(a+4b-a+4b)/2=sinasin4b
3)(sin^2a-tg^2a)/(cos^2a-ctg^2a)=sin^2a(cos^2a-1)*sin^2a/cos^2a*cos^2a*(sin^2a-1)=
=-sin^6a/-cos^6a=tg^6a