Let y'=y-2x.  Plug in the 49
integer points of
the form (a,b) for -3 <= a,b <= 3 into the right-hand side to get the
derivative at that point.  For example, the point (1,1) corresponds to
y'=1-2=-1.  Represent the derivative at each point with a short line
segment centered at that point whose slope is equal to the derivative.  In
the example, we would place a short line segment with slope -1 (minus 45
degrees) centered at the point (1,1).  See p.629 Figure 3 for an example.