# The Mathematics of Origami

Last week, the Department of Mathematics, through the outreach initiative, had a guest for the Recreational Mathematics Seminar. Laura Jimenez is a mathematician and a PhD candidate at the Department of Ecology and Evolutionary Biology at the University of Kansas. In college, she began to develop a passion for origami, and she was able to tie it with mathematics. When she was a master’s student, she worked in mathematical outreach and popularization and gave workshops about the mathematics behind origami.

At the Recreational Mathematics Seminar on Friday, November 15, Laura talked about how not only math is used in proving whether something is foldable or not and finding the folding pattern, but also origami can be a powerful tool for solving mathematical problems, such as solving a third-degree equation.

During the talk, the speaker presented the Huzita axioms, the mathematical principles of paper folding. The axioms list the seven operations that can be achieved by folding paper. The first axiom reads “Given two distinct points p1 and p2, there is a unique fold that passes through both of them.” The second one goes about placing a point into another; in this case the fold created turns out to be the perpendicular bisector to the segment joining the two points. Later on, Laura showed how one can trisect an acute angle by folding paper, in other words, by following the Huzita axioms.

The seminar was followed by a workshop where attendants learned how to fold a cube and a 12-pointed star of modular origami. Some would say that this type of origami is the most mathematical one. Modular origami pieces are made up by several sheets of paper. Each sheet is folded in the same manner, creating a unit with flaps and pockets. Then all pieces are put together by inserting flaps into pockets. This type of origami allows us to build geometrical objects such as the platonic solids.

Laura emphasized how origami is a great tool for teaching geometry.

On Saturday, our guest also ran our Girls Exploring Math Monthly workshop. Students explored the properties of buckyballs, polyhedra with regular pentagons and hexagons as faces. They analyzed the number of vertices, edges, and faces of each type, and came up with a relation between them. When building the origami model of a dodecahedron, the girls also looked at its graph representation and found a Hamiltonian path on it. Then, they used it to decide how to assemble the origami modules so that all the edges connected in every vertex had different colors (using modules of three different colors – it’s not as easy as you might think!).

The Recreational Math Seminar is gaining presence within the Department’s community, showing the most entertaining side of math. Recreational Math is a great way of getting undergraduate students interested in research. We will continue to bring more guests next term.