Question

Помогите, пожалуйста, с решением

Answer 1

$sin2\alpha-ctg\alpha=-cos2\alpha\cdot ctg\alpha$

$sin2\alpha-ctg\alpha=2sin\alpha cos\alpha- \frac{cos\alpha}{sin\alpha}=$

$\frac{2sin^2\alpha cos\alpha}{sin\alpha} - \frac{cos\alpha}{sin\alpha}= \frac{2sin^2\alpha cos\alpha -cos\alpha}{sin\alpha}=$

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

$-cos2\alpha\cdot \frac{cos\alpha}{sin\alpha}=-cos2\alpha\cdot ctg\alpha$