Question

помогите срочно надо

Answer 1

$ctg \beta -sin2 \beta =\frac{cos \beta }{sin \beta }-2sin \beta \cdot cos \beta =\frac{cos \beta -2sin^2 \beta \cdot cos \beta }{sin \beta }=\\\\=\frac{cos \beta (1-2sin^2 \beta )}{sin \beta }=\frac{cos \beta }{sin \beta }\cdot (sin^2 \beta +cos^2 \beta -2sin^2 \beta )=\\\\=ctg \beta \cdot (cos^2 \beta -sin^2 \beta )=ctg \beta \cdot cos2 \beta$