## Elementary Geometry for College Students (6th Edition)

$r=4.3 cm$
We draw an apothem. Then, we draw a triangle that extends to a corner of the pentagon closest to the apothem. This means the angle created is: $360/10=36$ We will call the apothem a. If we call the radius r, we can find: $cos(36)=a/r$ This means $r=a/cos(36)$ $r=4.3 cm$