Either Side
A wire in the shape of an equilateral triangle with sides of length 9 cm is placed on a flat piece of paper.
Imagine rolling a circular disc of radius 1cm around the inside of the wire.
What path would the centre of the disc trace out?
What if you rolled the disc around the outside of the wire?
Around the inside of the wire the result is another equilateral triangle:
Around the outside of the wire, the disc describes an arc of a circle as the disk rolls around each of the corners of the triangle:
