  A classic problem of the motion of a point mass (projectile) thrown at an
angle to the horizon is reviewed. The air drag force is taken into account with
the drag factor assumed to be constant. Analytic approach is used for
investigation. Simple analytical formulas are used for the constructing the
envelope of the family of the point mass trajectories. The equation of envelope
is applied for determination of maximum range of flight. The motion of a
baseball is presented as an example.
