Question

Докажите торжество, срочно

Answer 1

по формуле $\displaystyle ctg\alpha -ctg\beta =\frac{sin(\alpha -\beta )}{sin\alpha *sin\beta }$

$\displaystyle ctg2\beta -ctg4\beta =\frac{sin(2\beta -4\beta )}{sin2\beta *sin4\beta } =\frac{sin(-2\beta )}{sin2\beta *sin4\beta } =- \frac{sin(2\beta )}{sin2\beta *sin4\beta } =\frac{-1}{sin4\beta }$