ой, int tg(25y)dy=int sin(25*y)/cos(25*y)dy=
=[t=1cos(25*y),dt=-1/25*sin(25*y)]=-1/25*int dt/t=-1/25*ln|t|+C=
=-1/25*ln|cos(25*y)|
ln|v|=-1/25*ln|cos(25*y)|