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find the number of diagonals of a regular polygon whose interior angle measures 144

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Jeremiaid
Given:
              Interior angle of a polygon - [tex] 144^{o}

Find:
          Number of diagonals the polygon have

Solution:
               (Let us settle with the degrees later.)
      Interior angle =   [tex] \frac{180 (n-2)}{n) [/tex]
         144 = [tex] \frac{180 (n-2)}{n} [/tex]
         144n = 180 n - 360
        144n - 180n = 180n - 180n - 360
        [tex] \frac{-36n = -360}{-36} [/tex]
              n = 10

n = 10, that means that the polygon is a 10-sided polygon or DECAGON.
The remaining problem is its number of diagonals.
 
Number of diagonals = [tex] \frac{n(n-3)}{2} [/tex]
                                  = [tex] \frac{ 10(10 - 3)}{2} [/tex]
                                  = [tex] \frac{10 (7)}{2} [/tex]
                                  = [tex] \frac{70}{2} [/tex]
                                  = 35

Answer:

                The regular polygon that has an interior angle of 144 degrees has 35 diagonals.
          

                 
                              

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