When `a != 0`, there are two solutions to `ax^2 + bx + c = 0` and they are
`(d〖[〖NO〗_3〗^-])/dt=-(〖Vmax〗_((Nap) )×〖[〖NO〗_3〗^-])/(〖Km〗_((Nap) )+〖[〖NO〗_3〗^-])-〖kf〗_((〖〖NO〗_3〗^- ) )×〖[〖NO〗_3〗^-]`
