Tromino

All possible free trominos

A tromino is a polyomino of order 3, that is, a polygon in the plane made of three equal-sized squares connected edge-to-edge.^[1] When rotations and reflections are not considered to be distinct shapes, there are only two different free trominoes: "I" and "L" (the "L" shape is also called "V").

Since both free trominoes have reflection symmetry, they are also the only two one-sided trominoes (trominoes with reflections considered distinct). When rotations are also considered distinct, there are six fixed trominoes: two I and four L shapes. They can be obtained by rotating the above forms by 90°, 180° and 270°.^[2][3]

References

1. Golomb, Solomon W. (1994). Polyominoes (2nd ed.). Princeton, New Jersey: Princeton University Press. ISBN 0-691-02444-8.
2. Weisstein, Eric W. "Triomino". From MathWorld – A Wolfram Web Resource. Retrieved 2009-12-05.
3. Redelmeier, D. Hugh (1981). "Counting polyominoes: yet another attack". Discrete Mathematics 36: 191–203. doi:10.1016/0012-365X(81)90237-5.

External links

• Golomb's inductive proof of a tromino theorem at cut-the-knot
• Tromino Puzzle at cut-the-knot
• Interactive Tromino Puzzle at Amherst College