Suppose an arc is intercepted by a central angle of $\theta$ radians in a circle of radius r. The chord associated with that arc is the straight line segment joining the endpoints of the arc. The length of the chord, c, is given by
$c = r\sqrt{2-2 \cos( \theta)}$
A manufacturer of stop signs packs the signs into a circular drum, so that the signs fit snugly. Determine the radius of the drum given that length of each edge (chord) of the stop signs is 9 inches. (Recall that stop signs are regular octagons, 8-sided polygons with all sides and angles congruent.)
inches