Posted by JOY on Thursday, May 12, 2011 at 6:29am.
How do you calculate the lateral and surface areas of a cone whose height is 12 in and whose slant height is 15 in.

geometry  Reiny, Thursday, May 12, 2011 at 7:16am
Draw a cross section and you will have a rightangled triangle.
find the missing side which will be the radius of the base of the cone , r should be 9 in
You should have formulas for the surface area of a cone.

geometry  JOY, Thursday, May 12, 2011 at 7:49am
Could you show me the work for this one.
Thank you

geometry  Reiny, Thursday, May 12, 2011 at 8:24am
r^2 + 12^2 = 15^2
r^2 = 225144 = 81
r = √81 = 9
The surface area is made up of two parts,
the base, which is a circle, πr^2 and
the lateral surface (without the base) which has an area of πrs, where s is the slant height of 15 in
So total area is
πr^2 + πrs
= π(9^2) + π(9)(15)
= .....
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