Question

tg^2 альфа* cos^2 альфа + ctg^2 альфа * sin^2 альфа

Answer 1

=sin^2(a)/cos^2(a) *cos^2(a) + cos^2(a)/sin^2(a)*sin^2(a)=sin^2(a)+cos^2(a)=1

Answer 2

$tg^2a*cos^2a+ctg^2a*sin^2a= frac{sin^2a}{cos^2a}*cos^2a + frac{cos^2a}{sin^2a} *sin^2a=\\=sin^2a+cos^2a=1$