pentagon
There are 5 triangles in an heptagon
4-sided pyramid.
triangles, quadrilaterals, circles...
A square pyramid has 5 faces. The four side faces are triangles, and the base is in the form of a square. This pyramid has 5 vertices and 8 edges.
pentagon
There are 5 triangles in an heptagon
5 triangles are formed.
5 equilateral triangles.
5*3 - 3*4 = 15 - 12 = 3
4-sided pyramid.
A triangular prism
It has 9 edges, 5 faces and 6 vertices
triangles, quadrilaterals, circles...
It can form two quadrangles and three triangles. It has seven sides.
Imagine a house's roof -- two triangles joined by lines to their matching vertices. This gives you 6 vertices and only 5 sides.
They are polygons. They have fewer than 5 sides. They have fewer than 5 vertices.