There can be no closed 3D shape with only one square and 3 triangles.
One square and four triangles.
One square, 4 triangles.
A square pyramid has.
triangle and square 4 triangles one square
a square pyramid
the bottom one is a square and the other 4 are triangles
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.
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.