Question

Помогите, пожалуйста, с решением

Answer 1

$sin2alpha-ctgalpha=-cos2alphacdot ctgalpha$

$sin2alpha-ctgalpha=2sinalpha cosalpha- frac{cosalpha}{sinalpha}=$

$frac{2sin^2alpha cosalpha}{sinalpha} - frac{cosalpha}{sinalpha}= frac{2sin^2alpha cosalpha -cosalpha}{sinalpha}=$

$frac{-cosalpha(-2sin^2alpha+1)}{sinalpha}=frac{-cosalpha cdot cos2alpha}{sinalpha}=$

$-cos2alphacdot frac{cosalpha}{sinalpha}=-cos2alphacdot ctgalpha$