Question

Пожалуйста помогите другу нужно

Answer 1

$1+tg^2alpha =frac{1}{cos^2alpha } \ \ 1-tg^2alpha =frac{cos^2alpha -sin^2alpha }{cos^2alpha } =frac{cos2alpha }{cos^2alpha } \ \ frac{4tgalphacdot(1-tg^2alpha) }{(1+tg^2alpha)^4 } =frac{4tgalphacdot cos2alphacdot cos^4alpha }{cos^2alpha } =4sinalpha cdot cosalphacdot cos2alpha =\ \ 2sin2alpha cdot cos2alpha =sin4alpha$