Dissection of two polygons to one

Triangle — 2 × Triangle (5 pieces)

Square — 2 × Square (4 pieces)

Pentagon — 2 × Pentagon (9 pieces)

Hexagon — 2 × Hexagon (8 pieces with 2 turned over)

Heptagon — 2 × Heptagon (10 pieces with 1 turned over)

Octagon — 2 × Octagon (8 pieces)

Enneagon — 2 × Enneagon (19 pieces)

Discovered by Harry Hart (1877). This is a modification discovered by Ernest Irving Freese (1957).

Enneagon — 2 × Enneagon (16 pieces with 3 turned over)

Decagon — 2 × Decagon (16 pieces)

Hendecagon — 2 × Hendecagon (23 pieces)

Dodecagon — 2 × Dodecagon (10 pieces)

Discovered by Harry Lindgren (1964).

Tridecagon — 2 × Tridecagon (21 pieces with 6 turned over)

Tetradecagon — 2 × Tetradecagon (22 pieces with 7 turned over)

Pentadecagon — 2 × Pentadecagon (24 pieces with 7 turned over)

Hexadecagon — 2 × Hexadecagon (16 pieces)

Icosagon — 2 × Icosagon (20 pieces)

Icositetragon — 2 × Icositetragon (24 pieces)

Hexagram — 2 × Hexagram (11 pieces)

First discovered by Anton Hanegraaf (before 1990).

Octagram {8/2} — 2 × Octagram {8/2} (11 pieces)

Octagram {8/3} — 2 × Octagram {8/3} (12 pieces)

Dodecagram{12/2} — 2 × Dodecagram {12/2} (13 pieces)

Discovered by Greg Frederickson (1972).

Dodecagram {12/3} — 2 × Dodecagram {12/3} (12 pieces)

Discovered by Greg Frederickson (1972).

Dodecagram {12/4} — 2 × Dodecagram {12/4} (18 pieces)

Discovered by Greg Frederickson (1974).

Silver Rectangle — 2 × Silver Rectangle (2 pieces)

Golden Rectangle — 2 × Golden Rectangle (5 pieces)

Domino — 2 × Domino (5 pieces)

Greek Cross — 2 × Greek Cross (5 pieces)

Latin Cross — 2 × Latin Cross (9 pieces)