Question

cos^2t*tg^2t-Sin^2t*cos^2t

Answer 1

$cos^{2} t*tg^{2} t-sin^{2}t*cos^{2} t= frac{cos^{2}t*sin^{2}t}{cos^{2}t }-sin^{2}t*cos^{2}t=$
$sin^{2} t-sin^{2}t*cos^{2}t=sin^{2}t*(1-cos^{2}t)=sin^{2}t*sin^{2}t=sin^{4}t$