Question

What is the radius of a cone that has a lateral area of 70TT and a total surface area of 120TT?

A)50 units
B)50TT units
C)7.1 units
D)7.117 units

Answer 1

Explanation:

the lateral area of the cone is, well, the lateral area.

the total surface area of the cone is the lateral area plus the area of base circle.

so, the difference between both is the area of the base circle :

120pi - 70pi = 50pi

the area of a circle is

pi×radius²

and that is in our case

pi×radius² = 50pi

radius² = 50

radius = sqrt(50) = 7.071067812... ≈ 7.1 units

therefore, C is the right answer.