SAT Math: Geometry


If the sum of the interior angle of a regular polygon is 1,260 degrees, how many sides does the polygon have?

A.  6

B.   8

C.   9

D.   12

E.   14


Knowsys Method

Read the question carefully.  You know that in a regular polygon, all the sides have the same length and all of the angles have the same measure.

Identify the bottom line. # of sides = ?

Assess your options. You should use the polygon rule to find the answer.  The polygon rule is:

total degrees = 180(n - 2)  

The variable "n" represents the number of vertices, which is equal to the number of sides for a regular polygon. 

Attack the problem.

total degrees = 180(n - 2) 

1,260 = 180(n - 2) 

7 = n - 2

9 = n

 Loop back.  The number that you found represents both the number of angles and the number of sides, so you are done!


The correct answer is (C). 

This is a medium level question.


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