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1. 
   seraphina Student
   High School - 11th Grade

   Okay so to figure this out we will use the formula for finding the sum of interior angles of a regular polygon.

   Si= sum on interior angles

   n= number of sides

   Si = 180(n - 2)

   Since a heptagon has 7 sides, we just plug in 7 for "n"

   Si = 180(7 - 2)

   Si = 180(5)

   Si = 900

   If you need more help or if you want more practice, click on the smilie. Hope I helped =]

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   Posted by seraphina on Friday April 3, 2009 at 3:43 PM
   
   

2. 
   neela Teacher
   Graduate School

   eNotes Editor

   The heptagon is a seven sided closed plane figure.

   Take any point  O whithin the heptagon. Draw a line from each of the vertices of the heptagon to  meet at the point O.

   Now there are 7 triangles with  one  common vertex of the triangle coinciding at O.

   So, the sum of the angles of the seven triangles = 180*7=1260 degrees.                                     (1)

   Sum of the angles at the common vertex at O = 360 degrees , as it is equal to going about O one full round.             (2)

   From (1) and (2):

   (2)-(1) gives: 1060-360 =900 degrees is the sum of all the angles of the heptagon. Your question is answered with proof.
   

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   Posted by neela on Tuesday June 23, 2009 at 9:02 PM