Question

упростите выражение (1+tg^2a)*cos^2a-1

Answer 1

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