Question

Помогите срочноооо пож!!!

Answer 1

$dfrac{cos^4a-sin^4a}{(1-sina)(1+sina)} +2tg^2a= \ \ =dfrac{(cos^2a-sin^2a)(cos^2a+sin^2a)}{1-sin^2a} +2tg^2a= \ \ = dfrac{cos^2a-sin^2a}{cos^2a} + dfrac{2sin^2a}{cos^2a} = \ \ = dfrac{cos^2a+sin^2a}{cos^2a}= \ \ = dfrac{1}{cos^2a}$