What is the coefficient of x2 in the expansion of (x + 2)^3
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Given 
subject to the constraint 
Let
.
The gradient vectors of
and 
are:
and 
By Lagrange's theorem, there is a number
, such that
It can be seen that has local extreme values at the given region.
Let
The gradient vectors of
By Lagrange's theorem, there is a number
It can be seen that
Using the shell method, the volume is given exactly by the definite integral,
Splitting up the interval [0, 1] into 5 subintervals gives the partition,
[0, 1/5], [1/5, 2/5], [2/5, 3/5], [3/5, 4/5], [4/5, 5]
with left and right endpoints, respectively, for the -th subinterval
where . The midpoint of each subinterval is
Then the Riemann sum approximating the integral above is
(compare to the actual value of the integral of about 14.45)