Question

cos2α/1+cos²α, если tg=-1 помогите пожалуйста))

Answer 1

$frac{cos2 alpha }{1+cos^{2} alpha } = frac{cos^{2} alpha -sin^{2} alpha }{sin^{2} alpha } =( frac{cos alpha }{sin alpha } )^{2}-1=( frac{1}{ frac{sin alpha }{cos alpha } } )^{2}-1=( frac{1}{ tg alpha } )^{2}-1=$$( frac{1}{ -1 } )^{2}-1==(-1)^{2}-1=1-1=0$