Question

If r unit is the radius and 21 unit is the slant height of a right circular cone, then the total surface area is?​

Answer 1

Step-by-step explanation:

your ans will be

area =

$\pi \times r \times (r + \sqrt{h { }^{2} + r ^{2} } )$

where r is radius and h is height which is 21 ..

now put this value in your equation you will get your ans

Answer 2

Given data: Radius and slant height of a right circular cone is r and 21 unit respectively.

To find: The total surface area of a right circular cone.

Solution:

• The total surface area of a right circular cone is the sum of base area and lateral surface area.
• Base area$=\pi r^{2}$ and lateral surface area$=\pi rl$, where r is the radius and l is the slant height.
• Total surface area of a right circular cone$=\pi r^{2}+\pi rl$
• Substitute $r=r, l=21$
• Total surface area$=\pi r^{2}+\pi r(21)$
• Total surface area$=\pi r^{2}+21\pi r$
• Take the common value out,
• Total surface area$=\pi r(r+21)$
• Therefore, if r unit is the radius and 21 unit is the slant height of a right circular cone, then total surface area is $\pi r(r+21)$ $unit^{2}$.