Question

The diagram shows a solid cone. The radius of its base is $3.5$ cm and its surface area is $148.5$ cm${}^2$. What is its slant height(in cm)? $(\pi =\frac{22}{7})$

Answer 1

$CSA=\pi (rl+r^2)$

$\Rightarrow l=\left(\frac{C.S.A.}{\pi r}\right)-r$

$\Rightarrow l=[\left(\frac{148.5}{\frac{22}{7}\times \frac{3.5}{7}}\right)-3.5]$

$\Rightarrow l=10$