We need to find a numerical estimate for![]()
Consider
intervals
of width
with equispaced points![]()

![]()
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There exists
such that![]()
Using
, we can rewrite the composite Simpson's rule as
![]()
So, the composite Simpson's rule is 4th order accurate.
For example if
on the interval
with 10 intervals so
we can estimate an upper bound for the error for![]()
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