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 octagon
The answer to your question, is an Octahedron.
An octagonal pyramid
An octagonal pyramid.
Octahedron- A polyhedron with eight faces. All faces of a regular octahedron are congruent, equilateral triangles.
An octahedron
square pyramid
An octohedron has eight faces, all of which are triangles.
What polyhedron has eight sides and all of the are equilateral triangle?
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"
an octagon
A regular octagon
The answer is a pyramid.
octagonal pyramid :)
A pyramid.
The answer to your question, is an Octahedron.