Question

(cos^2y*ctg^2y+cos^2y)*tgy =

Answer 1

$(cos^2y*ctg^2y+cos^2y)*tgy =(cos^2y* frac{sin^2y}{cos^2y} +cos^2y)*tgy=\ =({sin^2y +cos^2y)*tgy=1*tgy= tg y.$