A (regular) pentagonal pyramid;
A (regular) pentagonal prism;
A truncated icosahedron (the shape of a soccer ball or the Buckminsterfullerene (fullerene) (C60), or "buckyball," molecule - if they sits on one of their pentagonal faces which could then be considered their base ).
A pyramid with a triangular base. The faces are 4 equilateral triangles.
There is a contradiction in your question. If the base has four equal sides then is it a square so not all the faces are Triangles. However if the base is a square and the rest of the faces are triangles then your object is a "Square-based Pyramid"
The description given fits that of a cube
A pyramid.
A rectangular pyramid is a solid (3-dimensional) figure that comes to a point opposite the base (like the Pyramids of Egypt.) Its base is a four-sided plane figure with right angles and opposite sides equal (a rectangle--or square for that matter).
The figure is a pyramid and the base is a square.
The answer is a pyramid.
octagonal pyramid
A pyramid with a triangular base. The faces are 4 equilateral triangles.
There is a contradiction in your question. If the base has four equal sides then is it a square so not all the faces are Triangles. However if the base is a square and the rest of the faces are triangles then your object is a "Square-based Pyramid"
A regular pentagon-based pyramid.
Not necessarily. The solid could be a square based cuboid (hexahedron).
Pyramid
A pyramid with a square base, or a triangular prism.
The description given fits that of a cube
A pyramid.
A rectangular pyramid is a solid (3-dimensional) figure that comes to a point opposite the base (like the Pyramids of Egypt.) Its base is a four-sided plane figure with right angles and opposite sides equal (a rectangle--or square for that matter).