A concave octagon has one of the angles pointing towards inside the polygon.
Icosahedron are a shape with 20 faces, 30 edges and 12 vertices. All the faces are triangles.
Hexagonal pyramids have 7 faces, 12 edges, and 7 vertices. The base is a hexagon. All of the other faces are triangular.
Scalene triangles have no angles equal, and no sides of equal length.
Rhombuses (rhombi) have 4 equal sides. Both pairs of opposite sides are parallel.
An irregular nonagon is a nine-sided shape that does not have equal sides or angles.
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