A solid frustum is of height 8 cm. If the radii of its lower and upper ends are 3 cm and 9 cm respectively, then its slant height is (a) 15 cm         (b) 12 cm        (c) 10 cm         (d) 17 cm

Explanation

`r_{1}=9 cm`

`
r_{2}=3 cm`

`
h=8 cm`


Slant height` =sqrt{h^{2}+(r_{1}-r_{2})^{2}} `

`
=sqrt{8^{2}+(9-3)^{2}} `

`
=sqrt{64+36} `

`
=sqrt{100} `

`
=10 cm`