In a frictionless hard-wall collision with a reflector so massive so
that its recoil may be ignored, the angle of incidence of the particle
to the reflector's surface will equal the angle of departure from the
reflector's surface. Under these assumptions, compute the
scattering angle 
, as defined in the figure, for a particle
hitting the reflector off-center, a distance b from the x-axis (b
is called the ``impact parameter''). Now, solve explicitly for b to
show that
Hint: Depending upon how you approach this problem, you may need
to make use of the trigonometric
identity to simplify your expression(s),
