Question

Докажите тождество ctgt(-t)/tgt+ctgt=-cos^2t

Answer 1

$\frac{Ctg(-t)}{tgt+Ctgt} =-\frac{\frac{1}{tgt}} {tgt+\frac{1}{tgt}}=- \frac{1}{tgt}: \frac{1+tg^{2}t} {tgt} =- \frac{1}{tgt}* \frac{tgt}{1+tg^{2}t}=- \frac{1}{1+tg^{2}t} =-Cos ^{2}t\\\\-Cos^{2}t=-Cos ^{2}t$

Тождество доказано