### Problems 26–32, on the attraction of a sphere, use Figure 14.18…

For the cone out to $r=1-z$, the average distance from the $z$ axis is $\bar{r}=\frac{1}{2}$. For the triangle out to $r=1-z$ the average is $\bar{r}=\frac{1}{3}$. How can they be different when rotating the triangle produces the cone?

### Problems 26–32, on the attraction of a sphere, use Figure 14.18 and the law of cosines $q^2=D^2-2\rho D\cos \varphi +{\rho }^2=u$.

This exercise builds on another exercise in its source book, which isn't shown here.

Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) · §14.4 Cylindrical and Spherical Coordinates, #25