Question

Find the volume of the
shaded part.

Answer 1

as already suggested, we can simply get the whole volume of the larger cone and then get the volume of the upper-smaller cone and if we subtract the volume of the upper-smaller cone, in essence making a hole in the larger cone, what's leftover is the shaded part.

`\stackrel{ \textit{\LARGE Larger} }{\textit{volume of a cone}}\\\\ V=\cfrac{\pi r^2 h}{3}~~ \begin{cases} r=radius\\ h=height\\[-0.5em] \hrulefill\\ r=4\\ h=10 \end{cases}\implies V=\cfrac{\pi (4)^2 (10)}{3} \\\\\\ \stackrel{ \textit{\LARGE Upper-Smaller} }{\textit{volume of a cone}}\\\\ V=\cfrac{\pi r^2 h}{3}~~ \begin{cases} r=radius\\ h=height\\[-0.5em] \hrulefill\\ r=2\\ h=4 \end{cases}\implies V=\cfrac{\pi (2)^2 (4)}{3} \\\\[-0.35em] ~\dotfill`

`\cfrac{\pi (4)^2 (10)}{3}~~ - ~~\cfrac{\pi (2)^2 (4)}{3}\implies \cfrac{160\pi }{3}-\cfrac{16\pi }{3}\implies \cfrac{160\pi -16\pi }{3} \\\\\\ \cfrac{144\pi }{3} ~~ \approx ~~ \text{\LARGE 150.80}~cm^2`