Question

find the curved surface area of a cone whose base radius is 5.6cm and slant height is 9cm.

Answer 1

Ans: In a cone,
Radius of the base,r =5.6 cm
Slant height,l = 9 cm
Therefore,
Curved surface area = πrl =22/7 ×5.6 × 9
=22/7 ×50.4
=158.4 sq.cm

Answer 2

Solution-

Surface area of a cone = Area of the curved surface + Area of the base.

Area of the curved surface, with slant height as L and c as circumference of the base is,

$Area=\frac{1}{2}\times L\times c$

The value of c can be calculated as,

$c=2\pi r$

Where,

r = Radius of the base = 5.6 c.m

$\Rightarrow c=2\pi (5.6)$

$\Rightarrow c=35.18$

$\therefore \text{Area of curved surface}=\frac{1}{2}\times L\times c=\frac{1}{2}\times 9\times 35.18=158.31\ cm^2$