Discussion
The slant height of the frustum of a cone having radii of two ends as 5 cm and 2 cm respectively and height 4 cm is
Answer: B
For a frustum the slant height spans the difference of the radii horizontally and the height vertically.
\[ l = \sqrt{h^{2} + (R - r)^{2}} \]
\[ l = \sqrt{4^{2} + (5-2)^{2}} = \sqrt{16 + 9} = \sqrt{25} = 5 \text{ cm} \]
It is the difference of the radii, not their sum, that forms the horizontal leg - using \( 5+2 \) would give \( \sqrt{65} \), the third option.
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