A)1-sin^2a/cos^2a b)1-cos^2a/1-sina c)(1+tg^2a)*cos^2a-sin^2a d)(ctg^2a+1)*sin^2a-cos^2a

а)1-sin^2A/cos^2A=sin^2A+cos^2A-sin^2A/cos^2A=cos^2A/cos^2A=1

b)1-cos^2A/1-sinA= sin^2A+cos^2A-os^2A sin^2A+cos^2-sin^2A=sin^2A/cos^2A=tg^2A

c)(1+tg^2A)*cos^2A-sin^2A= cos^2 a + sin^2 a - sin^2 a = cos^2 a

d)