The only thing I can come up with would be a tetrahedron. You could make a pyramid with a square (open) base, I guess.
equilateral triangles and regular pentagons
4.
It is a regular octahedron.
The answer depends upon what is meant by "have 3 triangles?" The definition of a pyramid is "a solid having a polygonal base, and triangular sides that meet in a point." (Random House Webster's Unabridged Dictionary) Typical pyramids have a 4-sided quadrilateral base and 4 triangular sides, which means that it can be loosely said to also "have" 3 triangles as well as "have" 4 triangles. A pyramid with a triangular base would also have 3 triangular sides. If we include the shape of the base as a side of the pyramid, then no pyramid would have exactly 3 "sides."
rhombus
Tetrahedron.
yolo
A square pyramid.
It is a tetrahedron pyramid
A tetrahedron
A pyramid.
Tetrahedron
A pyramid with a triangular base. The faces are 4 equilateral triangles.
Pyramid. Work: 4 sides (that you usually see) are triangles, the base (bottom) is a square
A square-based pyramid
You can make square pyramid.