Question

помогите пожалуйста алгебра

Answer 1

$frac{sin^4 alpha +2sin alpha cos alpha -cos^4 alpha }{2cos^2 alpha -1} = frac{-(cos^4 alpha -sin^4 alpha )+sdin2 alpha }{cos2 alpha } =\\= frac{-(cos^2 alpha -sin^2 alpha )(sin^2 alpha +cos^2 alpha )+sin2 alpha }{cos2 alpha } = frac{-cos2 alpha +sin2 alpha }{cos2 alpha } =\\=-1+ frac{sin2 alpha }{cos2 alpha } =tg2 alpha -1$