Solid mensuration . ..

the lateral area of a right circular cone is 40π sq.m . the base radius is 4cm. what is the slant height?

Curved surface area is πrl....where r is the radius and l is the slant height.

=> 0.04πl = 40π

=> l = 40π/0.04π = 40/0.04 = 4000/4 = 1000 metres

:)>

L .A = pi r l = 40pi--------------(I)
and r = 4 cm = 4/100 = 0.04m--------------------(II)
so pi*0.0 4*l = 40pi
or l = 40pi/ 0.04pi
= 1000 m answer
proof-----------------
lateral area = pi r l = pi x0.04 x1000= 40 pi m^2