Question

Помогите плиииз!!!! Доказать тождество!!!!

Answer 1

cos^2(a)/sin^2(a)-cos^2(a)=ctg^2(a)*cos^2(a)
(cos^2(a)*(1-sin^2(a)))/sin^2(a)= ctg^2(a)*cos^2(a)
ctg^2(a)*(1-sin^2(a))=ctg^2(a)*cos^2(a)
ctg^2(a)*cos^2(a)= ctg^2(a)*cos^2(a)