A square-based pyramid.
There can be no closed 3D shape with only one square and 3 triangles.
square-based pyramid
pyramid
A square pyramid is one that has a square base. This means there are four triangles, one triangle on each side of the square base.
the bottom one is a square and the other 4 are triangles
There can be no closed 3D shape with only one square and 3 triangles.
triangle and square 4 triangles one square
One square and four triangles.
square-based pyramid
a pyramid
A square pyramid has.
pyramid
a square pyramid
A square pyramid is one that has a square base. This means there are four triangles, one triangle on each side of the square base.
the bottom one is a square and the other 4 are triangles
A pyramid!!!! The base is a square. Each angle forming the base is 90 degrees. The four faces can each be equilateral triangles. Each triangular angle being 60 degrees. The base length and the triangular edges are all the same length.
A shape formed by four triangles would have to be a tetrahedron. But I believe that a tetrahedron can have at most three right angled triangles. One with four of them is, I think, impossible.