Question

докажите тождество 1/tg^2y+1- 1/ctg^2y+1

Answer 1

$\frac{1}{tg ^{2}y+1 } - \frac{1}{ctg ^{2}y+1 } = \frac{1}{ \frac{1}{cos ^{2}y } } - \frac{1}{ \frac{1}{sin ^{2}y } } =cos ^{2} y-sin ^{2} y=cos2y$