Question:
'The curved surface area of a frustum of a cone is $\pi l\left(r_{1}+r_{2}\right)$, where $l=\sqrt{h^{2}+\left(r_{1}+r_{2}\right)^{2}}, r_{1}$ and $r_{2}$ are
the radii of the two ends of the frustum and $h$ is the vertical height.
Solution:
Fasle
We know that, if $r_{1}$ and $r_{2}$ are the radii of the two ends of the frustum and $h$ is the vertical height, then curved surface area of a frustum
is $\pi\left(r_{1}+r_{2}\right)$, where $l=\sqrt{h^{2}+\left(r_{1}-r_{2}\right)^{2}}$.