[Four flat shapes are each made up of a combination of squares and triangles. The narrator reads out the onscreen text.]

NARRATOR: Question two. Which of these drawings is a net of a pyramid? Each of the nets has five faces, one of which is a square. The solid must therefore be a square-based pyramid. The square in each net must form the base. In order for the net to form a pyramid, there must be four isosceles triangles whose apexes must meet at one vertex when the solid is formed. The base of each isosceles triangle must form an edge with the square and hence the base of each isosceles triangle must be the same length as the side of the square.

The first net contains the square base and four isosceles triangles, but the four apexes of the isosceles triangles do not meet at the same vertex. And the base of each isosceles triangle is not the same length as the base of the square. This drawing is not a net of a pyramid.

The second net contains the square base and four isosceles triangles. But the four apexes of the isosceles triangles will not meet at the same vertex when the solid is formed. This drawing is not a net of a pyramid.

The third net contains the square base but does not contain four isosceles triangles. This drawing is not a net of a pyramid.

The fourth net contains the square base and four isosceles triangles. The base length of each isosceles triangle is the same as the side length of the square. The apexes of each of the four isosceles triangles will all meet at one vertex when the solid is formed. This drawing is a net of a pyramid.