.решить все 4 примерапожалуйстааааа)))

1) (1+tg^2 a)cos^2 a -1= cos^2 a+(sin^2 a/cos^2 a)*cos^2 a-1= cos^2 a+sin^2 a-1= 1-1=0; 2) 1-sin^2 a(1+ctg^2 a)= 1 -(sin^2 a+(cos^2 a/sin^2 a)*sin^2 a)= 1-(sin^2 a+cos^2 a)= 1-1=0; 3)1+tg^2 a+1/sin^2 a= 1/cos^2 a+1/sin^2 a= (sin^2 a+cos^2 a)/cos^2 a*sin^2a= 1/cos^2 a*sin^2 a; 4) (1+tg^2 a)/(1+ctg^2 a)= (1/cos^2 a)/(1/sin^2 a)= (1/cos^2 a)*sin^2 a= sin^2 a/cos^2 a= tg^2 a.