Daily Equation #3 - Spiral r = a*theta

This is Day 3 of my collection of printable equations. To see the whole collection, go to: http://www.thingiverse.com/thing:227210

For today's equation, we're moving to polar coordinates! By defining distance based on the angle, you can get beautiful symmetries in curves. The other advantage of polar coordinates is that, since theta and theta+360*n define the same rotational position, it's easy to define a curve with multiple y values for the same x value (vs. cartesian coordinates which requ