[tex]\bf \begin{array}{ccccccccc}
&&x_1&&y_1&&x_2&&y_2\\
% (a,b)
&&(~ 7 &,& 2~)
% (c,d)
&&(~ 5 &,& 4~)
\end{array}
\\\\\\
% slope = m
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{4-2}{5-7}\implies \cfrac{2}{-2}\implies -1[/tex]
since the sphere has a diameter of 20, its radius is half that, or 10.
[tex]\bf \textit{volume of a sphere}\\\\
V=\cfrac{4\pi r^3}{3}~~
\begin{cases}
r=radius\\
-----\\
r=10
\end{cases}\implies V=\cfrac{4\pi (10)^3}{3}[/tex]
