The area of the surface is given exactly by the integral,
![\displaystyle\pi\int_0^5\sqrt{1+(y'(x))^2}\,\mathrm dx](https://tex.z-dn.net/?f=%5Cdisplaystyle%5Cpi%5Cint_0%5E5%5Csqrt%7B1%2B%28y%27%28x%29%29%5E2%7D%5C%2C%5Cmathrm%20dx)
We have
![y(x)=\dfrac15x^5\implies y'(x)=x^4](https://tex.z-dn.net/?f=y%28x%29%3D%5Cdfrac15x%5E5%5Cimplies%20y%27%28x%29%3Dx%5E4)
so the area is
![\displaystyle\pi\int_0^5\sqrt{1+x^8}\,\mathrm dx](https://tex.z-dn.net/?f=%5Cdisplaystyle%5Cpi%5Cint_0%5E5%5Csqrt%7B1%2Bx%5E8%7D%5C%2C%5Cmathrm%20dx)
We split up the domain of integration into 10 subintervals,
[0, 1/2], [1/2, 1], [1, 3/2], ..., [4, 9/2], [9/2, 5]
where the left and right endpoints for the
-th subinterval are, respectively,
![\ell_i=\dfrac{5-0}{10}(i-1)=\dfrac{i-1}2](https://tex.z-dn.net/?f=%5Cell_i%3D%5Cdfrac%7B5-0%7D%7B10%7D%28i-1%29%3D%5Cdfrac%7Bi-1%7D2)
![r_i=\dfrac{5-0}{10}i=\dfrac i2](https://tex.z-dn.net/?f=r_i%3D%5Cdfrac%7B5-0%7D%7B10%7Di%3D%5Cdfrac%20i2)
with midpoint
![m_i=\dfrac{\ell_i+r_i}2=\dfrac{2i-1}4](https://tex.z-dn.net/?f=m_i%3D%5Cdfrac%7B%5Cell_i%2Br_i%7D2%3D%5Cdfrac%7B2i-1%7D4)
with
.
Over each subinterval, we interpolate
with the quadratic polynomial,
![p_i(x)=f(\ell_i)\dfrac{(x-m_i)(x-r_i)}{(\ell_i-m_i)(\ell_i-r_i)}+f(m_i)\dfrac{(x-\ell_i)(x-r_i)}{(m_i-\ell_i)(m_i-r_i)}+f(r_i)\dfrac{(x-\ell_i)(x-m_i)}{(r_i-\ell_i)(r_i-m_i)}](https://tex.z-dn.net/?f=p_i%28x%29%3Df%28%5Cell_i%29%5Cdfrac%7B%28x-m_i%29%28x-r_i%29%7D%7B%28%5Cell_i-m_i%29%28%5Cell_i-r_i%29%7D%2Bf%28m_i%29%5Cdfrac%7B%28x-%5Cell_i%29%28x-r_i%29%7D%7B%28m_i-%5Cell_i%29%28m_i-r_i%29%7D%2Bf%28r_i%29%5Cdfrac%7B%28x-%5Cell_i%29%28x-m_i%29%7D%7B%28r_i-%5Cell_i%29%28r_i-m_i%29%7D)
Then
![\displaystyle\int_0^5f(x)\,\mathrm dx\approx\sum_{i=1}^{10}\int_{\ell_i}^{r_i}p_i(x)\,\mathrm dx](https://tex.z-dn.net/?f=%5Cdisplaystyle%5Cint_0%5E5f%28x%29%5C%2C%5Cmathrm%20dx%5Capprox%5Csum_%7Bi%3D1%7D%5E%7B10%7D%5Cint_%7B%5Cell_i%7D%5E%7Br_i%7Dp_i%28x%29%5C%2C%5Cmathrm%20dx)
It turns out that the latter integral reduces significantly to
![\displaystyle\int_0^5f(x)\,\mathrm dx\approx\frac56\left(f(0)+4f\left(\frac{0+5}2\right)+f(5)\right)=\frac56\left(1+\sqrt{390,626}+\dfrac{\sqrt{390,881}}4\right)](https://tex.z-dn.net/?f=%5Cdisplaystyle%5Cint_0%5E5f%28x%29%5C%2C%5Cmathrm%20dx%5Capprox%5Cfrac56%5Cleft%28f%280%29%2B4f%5Cleft%28%5Cfrac%7B0%2B5%7D2%5Cright%29%2Bf%285%29%5Cright%29%3D%5Cfrac56%5Cleft%281%2B%5Csqrt%7B390%2C626%7D%2B%5Cdfrac%7B%5Csqrt%7B390%2C881%7D%7D4%5Cright%29)
which is about 651.918, so that the area is approximately
.
Compare this to actual value of the integral, which is closer to 1967.