A figure can tessellate only if its interior angle is a factor of 360. For an equilateral triangle, each interior angle is 60°; 360÷60 = 6, so this works.
For a regular hexagon, each interior angle is (6-2)(180)/6=4(180)/6=720/6=120; 360÷120=3, so this works.
For a regular pentagon, each interior angle is (5-2)(180)/5=3(180)/5=540/5=108; 360÷108=3.3. This does not divide evenly, so it does not work.
For a square, each interior angle is 90°; 360÷90=4, so this works.
