The surface area of a cone is 16.8pi in. the radius is 3 in what is the slant height

The first step in finding the surface area of a cone is to measure the radius of the circle part of the cone. The next step is to find the area of the circle, or base. The area of a circle is 3.14 times the radius squared (πr2). Now, you will need to find the area of the cone itself. In order to do this, you must measure the side (slant height) of the cone. Make sure you use the same form of measurement as the radius.

You can now use the measurement of the side to find the area of the cone. The formula for the area of a cone is 3.14 times the radius times the side (πrl).  

So the surface area of the cone equals the area of the circle plus the area of the cone and the final formula is given by:

SA = πr2 + πrl