This math fractions ClipArt gallery offers 5 illustrations of a three sided polygon broken into third slices. This includes images of individual slices, as well as the polygon with missing slices.
1/3 of a 3 sided polygon
2/3 of a 3 sided polygon
3/3 of a 3 sided polygon
3/3 of a 3 sided polygon with one piece detached
Illustration of a square divided into thirds. One third is shaded.