In mathematics, we often draw idealised pictures of real-world objects. Hence we simplify our drawings of geometric solids to lines, points and regions.
The diagram below shows how this is done for the drawing of a book.
The polyhedron is considered to be made of see-through material that allows the viewer to see all the edges of the prism.
Broken lines are used to represent those edges not normally visible to improve the quality of the drawing.
Below are several drawings of a triangular prism where the triangle is an isosceles right-angled triangle.