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2015-03-29T21:38:44+08:00

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Given:
               slant height of the frustum = 9 ft
               radii of the bases               = 5 ft and 7 ft
          
Find:
            Lateral Area and Total Area (I assume this is surface area.) of the right circular cone.

Solution:
(Let  \pi be 3.14.)

               Lateral Area =  \pi (R + r)s
                 
                          = 3.14( 7 ft + 5 ft) 9ft
                         = 3.14 ( 12 ft) 9ft
                         = 3.14 ( 108 ft²)
                        = 339.12 ft²

             Surface Area =  \pi  [s (R + r) + R² + r² ]
                                  = 3.14 [ 9 ( 7  + 5 ) + 7² + 5² ]
                                  = 3.14 [ 9 ( 12 ) + 49  + 25 ]
                                  = 3.14 [ 108 + 74 ]
                                  = 3.14 [ 182 ]
                                  = 571. 48 ft²
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