A pyramid.
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 pyramid with a triangular base. The faces are 4 equilateral triangles.
Tetrahedron
Triangular prisim. The three faces are rectangles, while the two bases are triangles.
triangular prism
The answer is a pyramid.
The figure is a pyramid and the base is a square.
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 tetrahedron.
octagonal pyramid
A pyramid with a triangular base. The faces are 4 equilateral triangles.
A regular pentagon-based pyramid.
Pyramid.
A pyramid.
Not necessarily. The solid could be a square based cuboid (hexahedron).
None it is impossible.
A cube is a solid figure with eight vertices and all faces of equal size.