# Chapter 11 - Section 11.2 - The Cosine Ratio and Applications - Exercises - Page 504: 33

$a = 10cos 36^{\circ}$

#### Work Step by Step

When we break a polygon into 10 separate right triangles, each triangle has an angle of 36 degrees in it. Using this angle and the fact that the radius is 10 inches, we find: $cos 36^{\circ} = \frac{a}{10} \\ a = 10cos 36^{\circ}$

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