Question

cos^2t-(ctg^2t + 1) * sin^2 t =

Answer 1

ctg^2(t)=cos^2(t)/sin^2(t);

раскрываем скобки, получаем: cos^2(t) - cos^2(t) - sin^2(t) = -sin^2(t).

Ответ: -sin^2(t).

Answer 2

  $cos^2t-(ctg^2t + 1) * sin^2 t = cos^2 t - frac{1}{sin^2 t} sin^2 t=cos^2 t-1=-sin^2 t$