tg^2 (a)+sin^2 (a) -1/ (cos^2 (a) (cos (3 a)+cos (a) / (2 cos

1) tg^2 (a)+sin^2 (a) -1/ (cos^2 (a)=sin^2 (a) /cos^2 (a)+sin^2 (a) -1/cos^2 (a)=(sin^2 (a) — sin^2 (a) -cos^2 (a)+sin^2 (a)*cos^2 (a) /cos^2 (a)=(cos^2 (a) (sin^2 (a) -1) /cos^2 (a)=sin^2 (a) -1=sin^2 (a) — sin^2 (a) -cos^2 (a)=-cos^2 (a) 2) (cos (3 a)+cos (a) / (2 cos (a)+2 sin^2 (a)=(4cos^3 (a) -3cos (a)+cos (a) /2cos (a)+2sin^2 (a)=(4cos^3 (a) -2cos (a) /2cos (a)+2sin^2 (a)=2cos (a)*(2cos^2 (a) -1) /2cos (a)+2sin^ (a)=2cos^2 (a) -cos^2 (a) -sin^2 (a)+2sin^2 (a)=cos^2 (a)+sin^2 (a).