## Girls’ Angle Bulletin, Volume 13, Number 5

At Girls’ Angle, we frequently have members who express interest in making their drawings look more realistic, and this often leads to a study of perspective drawing, which is a fabulous way to get into geometry. In this issue, we’re fortunate to feature an interview with Franklin & Marshall College Professor Annalisa Crannell, who recently wrote an entire book on perspective drawing together with Marc Frantz and Fumiko Futamura. And, special thanks to Princeton University Press, we include a two-page excerpt from their book, “Perspective and Projective Geometry.” Their book is highly engaging and offers a series of excellent perspective drawing exercises that are not only mathematically interesting, but also a lot of fun to do.

We have been incredibly fortunate to include a regular column, Needell in the Haystack, authored by Professor Deanna Needell on big data techniques. She is an amazing, benevolent force, and today, she’s also helping to fight the pandemic. However, in this issue, she writes about how bias creeps into mathematical analyses of data, which is an incredibly important and apt topic for our times. Normally, we remove her column from the electronic version, but we’re including the full article this time.

The cover might look like a perspective drawing, but it isn’t. It’s a design that Liliana Smolen and Isabel Wood created while the were playing around coming up with designs that illustrate mathematical identities. This issue’s Mathematical Buffet features four more of their designs. While Liliana and Isabel dreamed up these designs entirely from a blank white board, these particular designs have been seen before, and many more are collected in the books Proof Without Words: Exercises in Visual Thinking, by Roger Nelsen. The cover is a triangular version of the Fibonacci spiral. They even came up with a spiral that represents the mathematical constant e, but, unfortunately, there wasn’t enough space to include it. Perhaps you can come up with a way?

And we have our traditional Summer Fun Problem Sets. This summer, we present five: Cannonballs and Combinatorics by Girls’ Angle mentor Annie Yun, Tetrahedra with Congruent Faces by Ken Fan, Bernoulli Numbers by Matthew de Courcy-Ireland, Matrix Expedition by Girls’ Angle mentor Jasmine Zou, and Two Whole Squares by Ken Fan and Girls’ Angle Head Mentor Grace Work. As always, members and subscribers are encouraged to send us any questions and/or solutions.

We conclude with some Notes from the Club, which are authored by our Head Mentor Grace Work.

We hope you enjoy it!

Finally, a reminder: when you subscribe to the Girls’ Angle Bulletin, you’re not just getting a subscription to a magazine. You are also gaining access to the Girls’ Angle mentors.  We urge all subscribers and members to write us with your math questions or anything else in the Bulletin or having to do with mathematics in general. We will respond. We want you to get active and do mathematics. Parts of the Bulletin are written to induce you to wonder and respond with more questions. Don’t let those questions fade away and become forgotten. Send them to us!

Also, the Girls’ Angle Bulletin is a venue for students who wish to showcase their mathematical achievements that go above and beyond the curriculum. If you’re a student and have discovered something nifty in math, considering submitting it to the Bulletin.

We continue to encourage people to subscribe to our print version, so we have removed some content from the electronic version.  Subscriptions are a great way to support Girls’ Angle while getting something concrete back in return.  We hope you subscribe!