The electronic version of the latest issue of the Girls’ Angle Bulletin is now available on our website.

After reading *Stained Glass Angles* in Volume 7, Number 4, Marion Walter happened upon an amazing stained glass window by John Rose at the Eugene Public Library in Oregon. That inspired her to suggest a *Math Buffet* column featuring mathematically inspired stained glass windows. One thing led to another, and in this issue, we feature stained glass windows from 7 designers. The cover shows a detail of a stained glass window designed by Millie Wert, a graduate of Harpeth Hall. (Added January 27, 2015: For more math inspired stained-glass windows by students of Thaddeus Wert at Harpet Hall, please visit his blog.)

Next, comes the second half of Margo Dawes’ interview of Cathleen Morawetz, Professor Emerita at the Courant Institute of Mathematical Science at New York University.

Emily and Jasmine continue discussing *n*-pointed stars. Last issue, they showed that the sum of the tip angles of any 5-pointed star is 180 degrees. This time, they try to generalize to *n*-pointed stars, like the 7-pointed star at right. They end up in a discussion about definitions: just what is an *n*-pointed star anyway?

Pull out your compass and straightedge for this issue’s *Learn by Doing*. All of our *Learn by Doing* installments offer the opportunity to explore math through problem solving. The problems start out with the aim of gaining familiarity with the topic at hand and gradually probe deeper and become more challenging. Can you make it all the way through? If not and you’re a subscriber, don’t hesitate to email us for help.

Anna had so much fun exploring cross sections of a paraboloid of revolution, she decided to investigate cross sections of the graph of *z* = *xy*.

If you want to tell us anything about your mathematical explorations, we encourage you to email us about it.

In this issue, we’re beginning a mini-series on the derivative. There are many fine books and textbooks devoted to the subject of calculus. For example, there’s Courant and John’s *Introduction to Calculus and Analysis, Volume 1,* Rudin’s book *Principles of Mathematical Analysis*, and many, many more. Instead of attempting to produce our own textbook, we’re going to give a non-rigorous, but hopefully illuminating explanation. If one grasps local linearity, many results in calculus can be intuited and we hope to show how.

There’s more, including: a card game we call “Full Deck” that addresses the critical technical skill needed to learn how to multiply and divide with decimal numbers, an introduction to the choose function notation, and Notes from the Club where you can read a summary of Prof. Cornelia Van Cott’s recent visit to the club.

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!

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!

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