1. (sina+cosa)^2+(sina-cosa)^2 -2=
=sin²x+2sinxcosx+cos²x+sin²x-2sinxcosx+cos²x-2=2-2=0
2. (sinx+1/sinx)^2+(cosx+1/cosx)^2 -tg^2x-ctg^2x=
=sin²x+2+1/sin²x+cos²x+2+1/cos²x-tg²x-ctg²x=
=1/sin²x+1/cos²x+5-tg²x-ctg²x=1+ctg²x+1+tg²x+5-tg²x-ctg²x=7
3. (sin^2a-tg^2a)/(cos^2a-ctg^2a)=(sin²a-sin²a/cos²a)/(cos²a-cos²a/sin²a)=
=sin²a(cos²a-1)/cos²a :cos²a(sin²a-1)/sin²a=-sin^4a/cos²a*(-sin²a/cos^4a)=
=sin^6a/cos^6a=tg^6a