(C) The table   indicates   both    positive    and negative    values  for f   ′′(x).  f ′′(x)
for  a   linear  function    would   be  zero    for     all     x.  Both    quadratic   and
exponential  functions   have    no  change  in  concavity   for     all    x.   A   cubic
function    would   include a   change  in  concavity,  and f ′′(x) would   be  linear.
Both    of  these   properties  are indicated   in  the table   with    the given   points.
Therefore,  the function    could   be  a   cubic.
(A)  From    the     integral    we  get     a   =   −1,     b   =   3,  so 
Replace  x   with    xk  and
replace dx   with   Δx   in  the     integrand   to  get     the     general     term    in  the
summation.