'The curved surface area of a frustum of a cone is

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 $l=\sqrt{h^{2}+\left(r_{1}-r_{2}\right)^{2}}$.

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