The shape of the cross section formed from slicing the pyramid is called; a triangle
We are told that it is a pyramid with a base that is a pentagon with all sides the same length.
Now, the Pyramid's ap-ex is usually constructed by isosceles triangles. Thus, when they are sliced from its ap-ex to from the vertex, in the cross section a triangle will be formed, This triangle will be an isosceles triangle.
In conclusion, the shape of the cross section formed from slicing the pyramid is a triangle.
Read more about pyramid cross section at; https://brainly.com/question/10076762